96 



GERMINATION. 



inactive; too much heat destroys the vegetative power; the 

 extreme limits are between thirty-two and one hundred and 

 twenty-two degrees of Fahrenheit's thermometer. The presence 

 of air is as indispensable to the germination of seeds, or at least 

 to their development, as it is to the respiration of animals. It 

 acts through the means of the oxygen it contains ; seeds placed 

 in contact with this gas are stimulated in their germination. 

 Light, on the contrary, hinders or at least retards it much. 



46. The first phenomenon observed in germination is the 

 swelling of the seed and the softening of its envelopes ; the time 

 at which the latter burst varies in different plants ; the manner 

 of this rupture is either regular or irregular. From this moment 



Fig. 126. 



we observe the embryo,which 

 is at this period termed plan- 

 tule (diminutive plant), begin 

 to develope (figs. 126 and 

 127), we observe its two 

 extremities which constantly 

 grow in opposite directions ; 

 .j the gemmule, called the as- 

 cending caudex, is directed 

 towards the air and light ; 

 the radicle or descending 

 caudex tends to bury itself in 

 the ground. The substance 

 of the coty'ledons liquefies ; 

 it becomes milky and serves 

 for the nourishment of the 

 plantule; the perisperm un- 

 dergoes an analogous trans- 

 formation and appears to 

 perform the same function. 

 While the radicle, by pene- 

 trating the earth, gives rise 

 to delicate little ramifications, 

 the stemmule lengthens and 

 raises up the coty'ledons. 

 The gemmule is at once free 



d 



Fig. 127. 



Explanation of Fig. 126. Seed of a bean in a state of germination ; a, 

 the spermoderm split ; 6, coty'ledons ; c, radicle ; d, plumule. 



Fig. 127. The same bean in a more advanced stage of development; 

 a, radicle ; 6, collum or neck ; c, the stemmule ; </, the cotyle'donous 

 leaves. 



46. What is the first phenomenon observed in germination ? What is 

 the ascending caudex ? What is the descending caudex ? When does 

 germination cease ? 



