THE STEM 45 



plants. As is the case of roots, so with stems, man puts 

 some to his own use, and accordingly cultivates potato 

 plants and allows them to form their tubers, or stores of 

 food, which he utilises. 



Stems also serve as the means whereby plants climb. 

 In some cases for instance, convolvulus and beans the 

 ordinary stem twines about any convenient support ; in 

 others for example, the white bryony, passion flower, 

 grape vine, etc. portions of the stem are modified to 

 form special climbing organs, known as tendrils. 



The crocus affords another example of a stem acting 

 as a storehouse of food. The stem is here even more 

 specialised than the potato, and, as we shall see later, 

 contains not only a store of food, and leaf-buds, but 

 even the flowers which will come up in the spring after 

 it is formed, the whole being packed up in, and pro- 

 tected by, special, tough, scale leaves. 



It is of great interest to trace how what appear at 

 first sight very different and distinct plant structures are 

 really very much alike, and gradually pass into one 

 another. 



In the creeping jenny and many other plants we find 

 stems which trail over the surface of the ground but 

 bear leaves all along their length. In the strawberry 

 these ordinary creeping stems bearing leaves are 

 replaced by runners, with only small scale leaves. This 

 type is the best for the special work they perform of 

 spreading the plant from place to place. In the iris 

 and Solomon's seal, underground stems loaded with 

 food-reserve take the place of the strawberry runners. 

 The artichoke supplies the connecting link between the 



