GERMINATION 



935 



the plumule to light, most of the food is unnecessary and 

 may gradually decompose in the ground ; but if condi- 

 tions for autophytic nutrition are less favorable, much or 

 even all of the food may be used by the seedling. 



Aspects of germination external to the seed. The 

 earliest conspicuous external index of germination 

 is the rupture of the testa and the protrusion of 

 the embryo. The time necessary for such pro- 

 trusion, after the seeds have been exposed to 

 proper germinative conditions, varies from one or 

 two days (as in lettuce or mustard) to some weeks 

 or months (as in the date). Small seeds germinate 

 more quickly, as a rule, than do large seeds, prob- 

 ably because the foods are digested more quickly 

 through easy access to water and oxygen. Starchy 



seeds commonly germinate more quickly than do Monocot y l seedlings: 



1229, an onion seed- 

 fatty seeds, and much more quickly than do ling (AUium Ce pa) t il- 



seeds with " reserve cellulose." The rupture of lustrating epigaean 

 the testa, which usually becomes much softened germination ; note the 



curvature of the coty- 



and weakened by the absorbed water, may be i e( i on ^ w h ose tip re- 

 effected by the growing radicle or by the coty- mains within the seed 

 ledon, as in many monocotyls. Sometimes the (s) ' acting as an ab " 



sorptive organ; 1230, 



embryo emerges through thin spots, as in the the seedling of a date 

 coconut, or pushes out a loosely fastened plug palm (Phoenix dactyl- 

 of tissue. Usually the radicle is the first part of ifera ) in lon g itudinal 



section; note the re- 



the embryo to protrude, and this is doubtless ad- ma rkabie cotyledon (c) 

 vantageous, since most seeds contain enough food whose axis elongates 

 for considerable growth, while all of the water upon germination; one 



end of the cotyledon 



must come from without. Often (as in the (5') remains within the 

 cocklebur) the radicle is so situated that it is the seed, acting as an ab- 

 first part of the embryo with which the entering so " ptive rgan; t . the 



other end continues 



water comes in contact, 1 and the absorption of f or a time to enclose 

 water from the soil by the young root system the plumule (/>) and 

 usually is well initiated before the external de- ^^f^'"" 1 " 10111 

 velopment of the plumule becomes prominent. 



In some cases the cotyledons remain in the soil, especially where 

 these organs are the chief seat of accumulated food, as in oaks and 



1 The significance of the position of the radicle in the seed of the cocklebur is seen from 

 the fact that if a bit of the testa is removed near the tip of the cotyledons, growth begins 

 at that point, the radicle then being the last part to react. 



