Modifications of Tap Root System

To perform some secondary functions, roots undergo modifications. They are identified as tap root due to their origin from radicle and bearing root hairs. 

1. Fleshy/storage Tap Roots. Tap roots become swollen due to storage of food. Hypocotyl may also become enlarged and swollen. Secondary roots are thin and thread-like. They do not occur in the region of hypocotyl. These roots arise singly. The leaves are radical as they appear to arise from root directly. 

(i) Conical: Fleshy root is like a cone, being thickest towards the base (soil surface) and gradually tapering towards apex. Thread like secondary roots are found throughout the length of the root showing that fleshy part is tap root e.g., Carrot. 

(ii) Fusiform: The root is swollen like a spindle, being thickest in the middle and narrowing towards both apex and base. In Indian Radish only the base is formed of swollen hypocotyl. In English Radish the basal half is swollen hypocotyl while the apical half is swollen enlarged tap root Lei, edible part is formed by hypcotyl and tap root both. Here less than 2/3rd part of root is formed by hypocotyl. Secondary roots develop from the tap root part only. 

(iii) Napiform is like a ‘top’ or sphere that thins out abruptly at the apex; ln Turnip, the swollen part is hypocotyl. ln beet chakundar/red root the swollen part is formed jointly by hypocotyl and tap root. Secondary roots occur in tap root part. More than 2/3rd part of fleshy root is formed by hypocotyl. 

(iv) Tuberous: Tap root is thickened except at the base without producing a definite shape, e.g., Mirabilis. 

2. Nodulated (Tuberculated roots). ln legumes (e g., Pisum sativum, Cicer arietinum) the roots bear numerous irregular swellings called nodules or tubercles. The nodules are pinkish and contain nitrogen fIxing bacteria Rhizobium Both bacteria and legume are benehtted by this association called as Ciprocal symbiosis. Due to it legumes are rich in proteins and are used in crop rotation. Nodules are Dinkish due to a pigment leghaemoglobin which carry oxygen and provide anaerobic environment in nodules tor nitrogenase to fix nitrogen. These nodules are found on primary and secondary roots only. 


3. Pneumatophores:  Pneumatophores or respiratory roots are short, vertical and negatively geotropical (apogeotropic) roots which occur in mangrove plants (Halophytes of swampy saline areas near sea shores). The roots come out of swamp; Their upper ends bear lenticels (pneumathodes) for  Exchange of gases, e. g. Avicennia, Sonneratia, 


4. Buttress Roots. They are laterally compressed horizontal roots which travel along the ground , f0f some distance and provide extra mechanical support 9 g., Ficus elastica (Rubber Tree) Ficus religiosa Peepal) Bombax (Simbal) These roots are formed jointly by base of trunk and tap root.


5. Reproductive Roots. Some tap roots or their branches develop adventitious buds and help in  Vegitative reproduction, e. g., Daibergia, Populus 

6. Mycorrhizal roots. These roots of higher plants possess fungal hyphae (live symbiotically) which help them to absorb food as well protection against other fungi .Root hairs are absent. Fungal hyphae may act as root hairs. e.g. Pinus, Bitula

Stem Branching types

The pattern of arrangement of branches on stem is called branching. it provides proper place for each branch. Unbranched stem is called Caudex (= Columnar). Caudex is unbranched stout stem with scars and remnants of fallen leaves and crown of leaves e.g., palms; Culm is that caudex in which nodes and internodes are very well distinct (jointed stem). Nodes are solid and intemodes hollow. Sum culms are called wooden grasses e.g., Bamboos. 

Branching is of two types :

(ii Dichotomous : The growing point divides into two to form two similar branches e.g. Liver worts, Dictyota, Asclepias, Hyphaena. 

(ii) Lateral : Axillary buds form a lateral branch and apical bud remains non dividing. Branches develop from Iateral buds in two manners. 

(a) Racemose or Monopodiai Branching. Apical bud of the main stem grows indefinetly so that the main axis continues from base to the tip. This unbranched axis is calied monopodial axis ortrunk Lateral branches do not compete with the main axis. They develop acropetally (oldest towards the base and youngest towards the growing point). it gives pyramidal (excurrent) shape. e.g. Eucalyptus,Mustard, Casuarina, Pinus. 

(b) Cymose or sympodial Branching. Apical bud of the main stem has limited growth. it is then either used up or modified into a fiower/thom/tendrii. Further growth of axis is continued by one, two or more branches arising from axillary buds. Thus main axis is not produced by the activity of main apicai

bud but by many axillary buds, hence called sympodiai axis (sympodium). Accordingly, cymose branching is of three 

types ; 

(1) Uniparous or Monochasial Cyme. The terminal bud stops its activity or get modified into the flowerltendril/thorn. Further growth of the axis is continued by one axillary branch an'sing lateraliy from axillary bud. Soon its bud also stops growth and the process is repeated. The successive branches develop on either both the sides alternately (scorpioid, e.g., Grapevine) or on one side only (helicoid. e.g., Saraca). 

(2) Biparous or Dichasial Cyme. After the inactivity of the growing point of the parent axis, further growth is continued by two lateral (axillary) branches: Axis is multipodial, e.g., Viscum, Carissa, Mirabis, Datura. 

(3) Multiparous or Polychasial Cyme. After the inactivity of the growing point of the parent axis,further gorwth is continued by more than two 'laterai branches. Axis iis multipodial, e-g., Euphorbia helioscopia, E. tirucalli, Croton

Types of plants according to height, growth and duration of stem

According to texture, height, growth and duration of stems. plants are herbs, shrubs, trees, creepers, twiners, climbers and lianas.

Herbs- Herbs are small plants with soft and pliable stems. Herbs can be annual (e.g., Buttercup). biennial (e.g., Henbane) and perennial (e.g., Canna). 

Shrubs- Shrubs are perennial plants with medium height. woody stems but without any distinction of trunk. Shrubs have oftenly several branches of equal height arising from base and are called bushes. e.g., Capparis, Rose. 

Trees- They are tall perennial plants with a thick woody main stem or trunk. Trees are of three types: 

a) Caudex (= columnar). unbranched trunk with crown of leaves e.g., Coconut. Palm. Date Palm '. nalm like habit is called arborescent.

 b) Excurrent. Monopodial with one main stem or trunk from Loss to apex. Lateral branches giving a cone like appearance. e.g., Eucalyptus. 

c) Deliquescent. The "main stem or trunk is distinguishable only for some distance after which it is replaced by a number or large branches which form a dome-shaped crown e.g., Mango, Dalbergia. Ficus (Banyan). 

CuIm : is unbranched jointed stem with distinct nodes and internodes. Nodes are usually solid while internodes are hollow e.g.. Bamboo. 

Trailers: They are plants which spread on the ground without rooting at intervals, e.g., Tribulus , Euphorbia prostrata. 

Creepers: The plants spread on the ground. rooting at intervals, e.g., Strawberry. 

Twiners. They are weak-stemmed plants where the stem coils or twines around an upright support. in dextral or sinistral manner. This coiling is genetic. e.g., Ipomoea cairica (Railway Creeper). Quisqualis (Rangoon Creeper). 

Climbers. The plants climb up an upright support by special clinging or clasping structures like tendn’ls. roots and hooks.

Lianas (= Lianes). Woody twiners and climbers are called lianas. They are found in tropical even green forests. e.g., Phanera (= Bauhinia) , Hiptage. 

Epiphytes: Epiphytes are plants which live on other plants for space only. They are. therefore. also called space parasites, Angiospermic epiphytes commonly live on trees. e.g., Vanda, Dendrobium. They often possess hanging roots with hygroscopic outer spongy tissue called velamen to absorb moisture.Vanda is first terrestrial and then becomes epiphyte.

Types of plants based on fruiting pattern

Monocarpic: They are plants which flower and fruit only once in life. All annuals and biennials are monocarpic, Some perennial plants are also monocarpic, e.g- Agave, Bambusa tulda, Melocanna bambusoides. They die after bearing fruits. 

Polycarpic:They are perennial plants bearing blowers and fruits every year after attaining maturity. e.g-Mango. peepal. Mango shows biennial bearing i.e., one year fruiting is more and in next year, it is poor.

Types of Plants based on life span

Ephemeral: Plant that completes its life cycle within 4-6 weeks

Annuals: Plants complete their life cycle within one season e.g., buttercup. pea. Wolffia is smallest rootless annual. 

Biennials Plants complete their life cycle in two seasons growing vegetatively and storing food in the first season, flowering and fruiting in the second season. e.g., Henbane. Radish (in temperate areas). 

Perennials The plants survive for several years. They may be herbs shrubs or trees e.g., Canna, zizyphus. Mango. Agave Bambusa, Eucalyptus. etc. Some perennial plants live for several hundred years. e.g., Sequoia (1500 years), Bodhi tree (Ficus religoisa) at Gaya. Banyan tree (Ficus benghalensis) is almost immortal.