6 STRUCTURAL BOTANY 



certain shoots of the potato plant have become 

 completely modified, so as to lose all the more 

 obvious characters of shoots, and to bear a super- 

 ficial resemblance to roots. These changes are the 

 external manifestation of a complete alteration of 

 function. The potato tubers have given up the usual 

 functions of shoots, and become adapted to serve as 

 storehouses of food (chiefly starch) for the young 

 plants which will grow from the " eyes " next 

 year. 



If, then, we compare the potato plant with the 

 Wallflower, we find that, while in the latter the shoot 

 consists entirely of above-ground branches bearing 

 green leaves, in the potato plant certain parts of the 

 shoot are changed into underground colourless organs, 

 bearing scale-leaves, and ending in tuberous swellings, 

 which are storehouses of food. 



But we must not suppose that all underground 

 organs which serve this purpose are shoots. Turnips, 

 radishes, and dahlia tubers are also underground parts 

 of plants, and in function are similar to potato tubers, 

 but here the structure and mode of growth show that 

 we have to do with modified parts of the root. 



The comparison of various plants thus shows us 

 that quite different parts may be changed, so as to 

 serve the same function, and that the same part may 

 be modified to perform quite different functions. We 

 shall meet with plenty of examples of this later on, 

 but the instances just given will suffice to introduce 

 us to the second great division of the science of 

 Botany, namely, the Morphology of plants. This is 



