20 



BOTANY 



shoot superficial outgrowths hairs, scales, etc. and the important 

 reproductive structures, the sporangia. 



The Growing-point In unicellular plants, and in such simple 

 filamentous forms as Spirogyra and Oscillatoria, all the cells are 

 equally capable of fission; but in most plants there is a definite 

 region, the growing-point, to which the formation of new cells is 

 mainly restricted. The growing-point is usually terminal, but may 

 occasionally e.g. many Kelps be intercalary. The tissues at 

 the growing-point may owe their origin to the divisions of a single 

 apical cell (Fig. 6), or there may be a mass of initial cells of 

 greater or less size. 



Branching 



The plant-body usually branches, and this is often repeated until 

 very extensive branch systems arise, like those of trees or the tufted, 



closely branched 

 bodies of many 

 Seaweeds. There 

 are two principal 

 types of branch- 

 ing, the Dichot- 

 omous and the 

 Monopodial. 



Dichotomy 



Dichotomy is the 

 formation of two 

 branches by the 

 equal forking of 

 an original one. 

 The growing- 

 point is divided 

 vertically into 

 equal parts, each 

 of which be- 

 comes the grow- 

 ing-point of one of 

 the new branches 

 (Fig. 11, B). The 



FIG. 11. A, inflorescence of Linum Virginianum, showing COn \ m n Rock ' 

 monopodial branching. -B,dichotomously branched thallus weed (Fucus) and 

 of Riccia glauca, enlarged ; sp, sporogonia. C, leaf of many Liverworts 

 the Walking Fern, Camptosorus rhizophyllus, showing nT>p pmnmni-, w 

 adventitious bud at the leaf apex. (C, after GRAY.) 



amples of true 



dichotomy. If one of the branches grows less rapidly than the 

 other, as in the early leaves of many Ferns, the real nature of the 



. k 



