VASCULAR PLANTS 241 



nemo) of branching green cell threads, which spreads 

 and often persists for a long time on damp soil. 

 From the protonema leafy moss plants arise by budding. 

 Vegetative Reproduction. Both Mosses and Liver- 

 worts spread largely by vegetative reproduction. The 

 thalli of Liverworts branch freely as they creep on 

 the soil, and the older parts, from which the branches 

 have arisen, gradually die off, so that the branches, 

 which have sent out rhizoids from their under surfaces, 

 become detached independent plants. In the Mosses 

 branching often takes place towards the base of the 

 shoot, and the lateral branches, creeping on or in the 

 soil, become attached by rhizoids, their tips growing 

 up into the air. The decay of the older part of the 

 shoot makes the new shoots independent plants. 

 Very many Mosses branch at the base in this way, 

 and the aerial shoots so produced grow up in close 

 neighbourhood, their tips forming the surface of the 

 characteristic moss tufts or cushions. 



Vascular Plants (Pteridophytes and Seed Plants). 

 The plants above the Mosses in the scale of adaptation 

 to terrestrial life are marked by several great steps in 

 advance. First they have true roots instead of rhizoids. 

 These are branches of the plant body many cells thick 

 which enter the soil, branch and form very efficient 

 organs for fixing the plant and absorbing water and 

 salts from the soil. The branches of the root are 

 comparable with the branches of the shoot, and like 

 them consist of complicated tissue structures, but 

 they differ from them in several important respects. 

 We shall have to consider these differences in detail 

 in later chapters. Here we need only note that roots 

 are colourless, and that they often bear root hairs, 

 which are tubular outgrowths of the surface cells 



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