192 



A TEXTBOOK OF BOTANY 



[Ch. IV, 11 



where the nearly glol)ular storage stem is commonly mis- 

 taken for, ami called, a bulb (page 73). All of these 

 stems produce roots, and also give rise to the foliage ; 

 but cases occur in which food-storage complet-ely displaces 



the foliage-supporting function, 

 and also the production of roots. 

 Then we have a new organ, ex- 

 emplified in the common potato, 

 the stem nature of which is 

 attested by the eyes, which are 

 axillary buds subtended by small 

 scale leaves. Such an organ, 

 rotund \\-ith accumulated food, 

 and composed mostly of thin- 

 walled rounded storage cells of 

 the great]}' developed pith and 

 cortex, is called a tuber, of which 

 many forms occur among plants. 

 Another important special func- 

 tion of stems is represented in 

 tendrils, \\'liicli liave the same 

 elongated slender forms, move- 

 ments through the air, thigmo- 

 tro]nc twining about a support, 

 and spiral shortening, already 

 described in leaf tendrils (page 

 77). Passion Mne, AVild Cu- 

 cumber, and Grape Mnes have 

 13G), which are more abundant and 



Fii.:. loG. — Teiiilrils, finm 

 axillary budw, in a Mexir-in 

 Passijiora. 



Compare also Fig. .52. Tho 

 tendriLs of Grape Vine and all 

 of the Gourd family (Sqi]a.sh, 

 Wild Cucumber), reijre.sent the 

 main .stem, the further p:ro\vth 

 taking place from the axillary- 

 bud. " (After Gray.) 



stem tendrils (Fig. 



perfect in form than leaf tendrils, perhaps liecause sujiport 



is a more natural function of stems than of leaves. 



Stems also become transformed into ftpincs, which are 

 sometimes very large, as in Honey Locust (Fig. 137). The 



