STEMS. 



49 



least possible surface is 



presented by a plant of 



given bulk, — that is, in 



the form of a sphere or an 



egg-shaped mass. This, 



above ground, corresponds 



to the corm or solid bulb 



of the crocus and the Indian 



turnip among underground 



stems. Other cactuses are 



more or less cylindrical or S 



prismatic, others still con- 

 sist of flattened joints, but 



all agree in offering much 



less surface to the sun and 



air than is exposed by an 



ordinary leafy plant. 



73. Leaf-like Stems. — 



The flattened stems of some 



kinds of cactus are sufii- 



ciently like fleshy leaves 



to pass for leaves among people who are not botanists, but 



there are a good many cases 

 in which the stem takes on a 

 strikingly leaf-like form. The 

 common asparagus sends up in 

 spring shoots that bear large 

 scales which are really reduced 

 leaves. Later in the season, 

 what seem like thread-like 

 leaves cover the much- 

 branched mature plant, but 

 J XX. these green threads are actually 



Fie. 36.— I, Bulb of Hyacinth. II, the minute branches, which per- 



same split lengthwise. 



Fig. 35. —A Six-ireeks'-old Potato Plant 

 gr.own from the Seed. 



a, b, upper branches, cut off ; d, cotyledons ; 

 e, underground stems, springing from huds 

 in the axils of the cotyledons ; /, g, tubers 

 developed from ends of underground stems 

 or from axils of scales borne upon them ; 

 h, roots. 



