INTRODUCTORY LESSONS. 



IX 



tube formed by the united petioles, 

 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 

 plumule meanwhile, as shown in /, 

 remains dormant in the bottom of 

 the tabular 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 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 we 

 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 

 accouiit 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 

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

 at 6, 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 pushed 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 

 at c and d. In one instance a sprout measured seven inches irom 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. 



