CHAPTER IV. 



THE STEM OF THE SUNFLOWER. MORPHOLOGY AND 

 HISTOLOGY. 



THE present chapter deals with the structure of stems, 

 and for the sake of convenience this part of the plant- 

 body is studied in the sunflower instead of in the bean or 

 pumpkin. The sunflower, Helianthus annum, is a near 

 relative of the Jerusalem artichoke, H. tuberosus, and what 

 is here said applies, speaking generally, to both. 



The germination of the sunflower is of the same 

 general type as that of the pumpkin; the embryo has a 

 pair of large fleshy cotyledons loaded with reserve matter, 

 which like those of the pumpkin expand above ground 

 and function as leaves, that is to say, they become green 

 with chlorophyll and they assimilate. Between the coty- 

 ledons is the minute plumule ; it bears a number of 

 undeveloped leaves crowded together, and surrounding 

 a growing point. It is in fact a bud which will lengthen 

 out into a tall stem on which fully developed leaves will 

 take the place of the semi-developed ones now clothing it. 

 The growing point at the extremity of the plumule differs 

 in detail from that of the root ; it has for instance 

 D. E. B. 4 



