298 A TEXTBOOK OF GENERAL BOTANY 
rotted or have been injured in some other way. This explains 
why the germination of many seeds is hastened by making 
holes in the hard seed coats. A period of rest is, however, 
by no means confined to such seeds as have impervious coats, 

‘ 
Fre. 303. Seed and germination of seedling of Indian corn 
Above, section of ungerminated seed and a seed in which the plumule and radicle 
are pushing out: e, endosperm ; s, cotyledon, or scutellum ; p, plumule ; 7, rad- 
icle (x 13). Below, germination of seed (x 2) 
as the necessity for a period of rest is frequently characteristic 
of the seeds themselves. It would appear that some metabolic 
change must take place in such seeds before they are ready for 
germination. 
Seeds in a dormant condition can withstand much greater 
extremes of heat and cold than can seedlings or mature plants. 
