146 



THE STEM PROPER 



208. Runners and Stolons, of which we have familiar 

 examples in the strawberry and currant respectively, are 

 stems or branches by which plants 

 propagate themselves above ground 

 as readily as by rootstocks under- 

 ground. Suckers are shoots from 

 adventitious root buds. The rose, 

 raspberry, blackberry, and asparagus 

 are propagated almost entirely by 

 their means. The little shoots, called 

 by gardeners scions, that spring up 

 around the foot of apple and pear 

 trees, and many others, have a simi- 

 lar origin. 



289. — Orange hawkweed ' 



with runners. 209. Modifications of the Stem. — 



Like leaves, the stem is subject to many modifications, 

 and is made to serve various purposes 

 other than its normal ones. With some 

 of these we have already become 

 acquainted in its underground condition. 

 Aerial stems frequently serve like pur- 

 poses. The sugar cane carries a rich 

 supply of sweets in its juicy internodes, 

 and cabbage stalks also are well stocked 

 .with food before flowering. In the 

 cactus family, which inhabit dry and 

 desert regions, where the scanty mois- 

 ture they draw from the earth would be 

 too rapidly exhaled from the expanded 

 surface of leaves, the foliage has either 

 disappeared altogether or been reduced 

 to mere spines, while the greatly thick- 

 ened stems have taken upon themselves 

 the triple office of leaf, stalk, and store- 

 room. Examine a potted cactus, or a 

 joint of the common prickly pear, and notice how the 

 whole plant has been compacted into a form that exposes 



m^ 



290. — Melon cactus, 

 showing greatly con- 

 densed stem for the 

 storage and preserva- 

 tion of moisture. 



