CHAPTER XI. 



MODIFICATIONS OF FORM IN THE VEGETATIVE 

 SYSTEM OF THE HIGHER PLANTS. 



It has been seen that the primary construction of the Higher Plants is 

 according to a general and uniform plan (p. 14). But the scheme may 

 be worked out in detail in very different ways. Either the root or the 

 shoot, or both, may vary in form and proportion in different plants. 

 Such differences are clearly related to the conditions under which the 

 plants grow. Since it is possible in very many cases to see that the 

 particular form taken is suitable for successful life under corresponding 

 particular conditions, such forms are described as being specialised, or 

 adapted to them. Those special modifications of form which lead to 

 success are described as adaptations, and will be so grouped here : 

 though with the same reservation as to causality as that expressed at 

 the close of the preceding chapter with reference to internal structure. 



Plants may be recognised as being thus adapted to the medium in 

 which they grow ; as, for instance, in water or in air : to other physical 

 conditions, such as the action of gravity, or the direction of light : to 

 the climate to which they are exposed, hot or cold, dry or moist, 

 equable or with marked seasons, quiescent or stormy : or to the 

 soil which provides them with requisite supplies : or they may 

 show special features which enable them to take advantage of other 

 surrounding circumstances. Prominent examples of this are seen in 

 plants which straggle or climb over others ; or in those which, by taking 

 to some irregular form of nutrition, derive advantage from their 

 neighbours as parasites, or in other ways. Such modifications of 

 form according to circumstance often lead to difficulties in recognition 

 of the category of parts to which the modified organs rightly belong. 

 A stem or even a root may carry out photosynthesis. A leaf may 

 be effective only for climbing, or for protection. It becomes therefore 

 b.b. 193 N 



