I.] GERMINATION 9 



of a pair of cotyledons or a single endosperm. There 

 are other minor differences in arrangement that need 

 not concern us ; there are also very interesting variations 

 in the way the root develops, in the origin of secondary 

 roots, side buds, etc., etc., and again in the character of 

 the cotyledons and the way they develop above ground, 

 but these points do not bear directly on nutrition, and 

 the student must follow them up for himself. 



We may now proceed to examine the conditions 

 which favour or are necessary to the germination of the 

 seed. In the first place, moisture is required ; dry seeds 

 can be kept a considerable time without apparent change, 

 it is only when the embryo has absorbed sufficient water 

 to get some of its soluble constituents into solution that 

 growth can begin at all. Hence a seed must be sown 

 in a sufficiently moist soil and the supply of moisture 

 must be maintained until the plant is established ; more- 

 over, moisture must reach the embryo inside the seed 

 coat, yet in some cases the seed coat offers a considerable 

 resistance to the passage of water through it. Every 

 seed possesses a fine passage through the seed coat, 

 called the micropyle, but in many cases soon after the 

 seed is ripe the micropyle becomes closed by the 

 shrinkage of the seed coat, which itself also grows 

 impervious to water. Hence follows a great delay in 

 germination, which may not take place indeed for a 

 year or longer until the seed coat has wholly decayed 

 away. With many garden plants, e.g. the auricula and 

 the hellebore, germination will take place in a few days 

 if the seeds are sown directly they are ripe, but if once 

 they are dried off and stored before sowing they will 

 probably remain dormant for a year in the seed pans 

 and then begin to germinate slowly or at irregular 

 intervals. In any sample of clover seed a certain 

 number of " hard " seeds will always be found which 



