32 



BOTANY OF CROP PLANTS 



3, Bulbs. — A bulb is an underground stem. The common 

 onion is a typical example. A median, lengthwise section 

 (Fig. 14) of the onion bulb, shows a small, cone-shaped stem 



upon which are numerous, 

 fleshy leaves that are over- 

 lapping and quite rich in food 

 material. Here, too, there is 

 a terminal bud, and kteral 

 buds occasionally in the leaf 

 axils. Bulbs are vertical 

 stems, thus differing from the 

 horizontal direction of growth 

 of rhizomes. 



4. Corms. — A corm is a 

 short, solid, vertical, under- 

 ground stem. It is typically 

 exempHfied in gladiolus. 

 Corms are usually flattened 

 from top to bottom, and bear 

 a cluster of thick fibrous 

 roots at the lower side, and a 

 tuft of leaves on the upper 

 side. Corms are storage 

 organs. 



5. Runners (stolons). — 

 These resemble rhizomes in 

 that their direction of growth 

 is horizontal. In the straw- 

 berry plant, the branches that arise from the axils of the 

 closely set leaves are called "runners." They are slender 

 stems, growing along the ground surface; they have long 

 internodes, and produce leaves, flowers and roots at the 

 nodes. Runners are used as a means of propagating the 



Fig. 14. — Median lengthwise section 

 of common onion bulb. 



