420 REVIEW AND CONCLUSION 



out of recognition, as in palms and grasses. Stems 

 may be thick and erect, or slender and creeping on the 

 ground or climbing up trees. When required to store 

 food and water during an off season, parts of both 

 roots and shoots taay be developed as tubers, rhizomes 

 or bulbs. In the case of epiphytes there may be two 

 different kinds of roots, a clinging and an absorptive, 

 on the same plant. Far reaching adaptations are found 

 in plants which inhabit dry and desolate regions, one 

 or two of which have been referred to in chapter xv. 

 We find among fruits and seeds all sorts of variations 

 to aid in dispersal of the seeds, and the most interesting 

 of all are those connected with the visits of insects to 

 flowers encouraged for the sake of the embryo. 



All these adaptations are specific, that is they belong 

 to the species and are not brought about in the lifetime 

 of the individual plant itself, though abnormal condi- 

 tions may prevent them appearing to a certain extent 

 (pp. 172-5). 



But the individual plant itself reacts to the envi- 

 ronment and always, as far as we can see, to a useful 

 end. Shoots react to gravity by growing upwards, 

 and to light by bending towards it. In darkness 

 they grow faster and longer, thus bringing the food- 

 making leaves to the light ; and at the same time the 

 leaves, useless in the dark, do not grow to their full 

 size, and the chlorophyl is not developed, the shoot 

 having a pale and sickly appearance (etiolated). Roots, 

 on the other hand, are induced by the same external 

 force, gravity, to grow downwards, and are attracted 

 also by moisture ; fixation in the ground and the absorp- 

 tion of water being their most important functions. 



