INTRODUCTORY LESSONS, ix 
tube formed by the united petioles, 
or stems, of the thick cotyledorts, 
and only tipped by the radicle— 
penetrates 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 belowe. In this 
wonderful way the plumule bud is 
deeply planted together with nour- 
ishment (stored in the radicle) which, 
af 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 they germinate early, and in 
the manner of other seeds, Jack Frost may nip them.* 
* Dr. Asa Gray, who first experimented with 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 were elevated two or three 
inches above the surface of the soil [the dotted line S represents the surface of the ground for figures 
u,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. 14 of second edition. The plants came up about four inches from 
where the seeds were planted, the plumule being pashed laterally that distance by the elongation of the 
cotyledon petioles. Such inexplicable behavior stimulated to further observation, which resulted in 
the discovery that naturally planted seeds, unhampered by boxes or pots, usually grow as represented 
atcandd, In one instance a sprout measured seven inches from the plumule to the cotyledons! The 
hairs at e probably help the sprout to penetrate the soil, by fastening on to the surface crust. Curiously 
enough, growing sprouts underground frequently avoid obstacles without touching them. 
