DISTRIBUTION OF SPORES AND SEEDS. 36 1 



ing also prevents the visits of any insects except those flying 

 at that particular season. 



III. Adaptations to the distribution of seeds. 



489. After the ripening of the seed various devices and 

 forces operate to scatter them at as great a distance as pos- 

 sible from the parent, so that the young plants will not come 

 into competition with the old ones or with each other. This 

 object, which is secured in lower plants by the distribution 

 of the spores, can only be attained in seed plants by scatter- 

 ing the seed, because the megaspore is not set free ; the ga- 



Fig. 405. — Elastic valves for slinging seeds. A, fruit of wild geranium (G. palustre) 

 with persistent calyx. The five carpels surround an elongated torus, from which they 

 break first at bottom ; curling upward suddenly they sling the seed out of the basal 

 part which has cracked along the inner side. B, fruit of touch-me-not (Impatiens 

 noli-me tangere), one sound, the other bursted. The carpels have curled up elasti- 

 cally from the base and slung out the seeds. Natural size.— After Kerner. 



metophyte is consequently developed within the sporophyte ; 

 and the embryo sporophyte is likewise enclosed by the old 

 sporophyte (See T 408.) 



