INTRODUCTOEY LESSONS. 



IX 



tube formed by the united petioles, 

 or stems, of the thick cotyledons, 

 and only tipped by the radicle — 

 penetratesi the ground to a depth, 

 usually, of four or five inches. The 

 plumule meanwhile, as shown in /, 

 remains dormant in the 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 

 becomes a tuber. Meanwhile the 

 plumule begins its upward growth, 

 splitting the petioles apart, and usu- 

 ally escaping from between them, as 

 shown in the figure below c. In this 

 wonderful w^ay 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 w«. 

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

 frost will kill the young plant. If the seeds wait till warm weather to 

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

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



* Dr. Aea Gray, who first experimented yrith these seeds, found them to grow as represented at a, in 

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

 account of some obstruction, probably the bottom of a small pot, the seeds wel-e 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 different results — shown 

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

 where the seeds were planted, the plumule being pushed laterally that distance by the elongation of the 

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

 the discovery that naturally planted seeds, unhampered by boxes or pots, usually grow as represented 

 at c and d. In one instance a sprout measured seven inches from the plumule to the cotyledons! Th» 

 hairs at « probably help the sprout to penetrate the soil, by fastening; on to the surface crust. Curiouslj 

 enough, growing sprouts underground frequently avoid obstacles without touching them. 



