INTRODUCTORY LESSONS. 



IX 



tube formed by the united i:)etioles, 

 or stems, of the thick cotyledons, 

 and only tipped by the radicle — 

 penetrates the ground to a depth, 

 usually, of four or five inches. The 

 2)lumu]e meanwhile, as shown in/*, 

 remains dormant in tlie bottom of 

 the tubular sprout. "When the pe- 

 tiole growth ceases, the radicle grows 

 rapidly by absorbing the nourish- 

 ment stored in the cotyledons, and 

 Ijecomes a tuber. Meanwhile the 

 plumule begius its upward growth, 

 splitting the petioles apart, and usu- 

 ally escaping from between them, as 

 showm in the figure below c. In this 

 Avonderful way the plumule bud is 

 deeply planted together with nour- 

 ishment(stored in the radicle) which, 

 if necessary, can be used to aid its 

 first growth. The reason for this curious behavior is obvious, when Wv 

 know that ground squirrels are fond of these seeds, and that a severe 

 frost will kill the young j^lant. If the seeds wait till warm weather to 

 sprout, hungry rodents may find them; if they germinate early, and in 

 the manner of other seeds, Jack Frost may nip them.* 



'■-■ Dr. Asa Gray, who first experimeuted with these seeds, found them to grow as represented at a, ia 

 the figure [reduced one fourth from Fig. 43, Botanical Text-book, edition of 1879]. Evidently og 

 a>couLt of some obstruction, probably the bottom of a small pot, the sieds were elevated two or threa 

 inches above the surface of the soil [the dotted line S represents the surface of the ground for flgurea 

 a, b, and c]. My experiments with seeds planted in shallow boxes gave very diflorent results — shown 

 at h, which is a reduced copy of Fig. 14 of second edition. The plants came up about four inches from 

 where the seeds were planted, Uie plumule being pash<"d laterally that distance by the elongation of the 

 cotyledon petioles. Such inexplicable behavior stimulated to further observation, which resulted iu 

 the discovery that naturally plan:ed seeds, unhampered by boxes c r pots, usually grow as represented 

 at c and d. In one instance a sprout measured seven inches Irom the plumule to the cotyledonsi Tlu 

 hairs at e probably help the pprout to penetrate the soil, by fastening on to the surface crust. Curiouslj 

 <anougb, growing sprouts underground frequently avoid obstacles without touching them. 



