25 



CHAPTER V. 



GERMINATION, ROOT GROWTH, STRUCTURE, 

 AND FUNCTIONS, 



If a living seed be placed in the soil and be supplied with 

 moisture and warmth, and exposed to fresh air, germination 

 will ensue. The range of temperature between which this is 



Fig. ^-2.— Ricinus cojninnnis. I. longitudinal section 

 of ripe seed. //, germinating seed, the cotyledons 

 still within the spermoderm, shown more distinctly 

 in A and B : j, spermoderm ; e, endosperm ; c^ coty- 

 ledon ; hc^ hypocotyledonary portion of axis ; nv, 

 primary root ; 11/ ., lateral rootlets ; x, the caruncle 

 (or aril), a peculiar appendage to the seeds of E^i- 

 phorbiacetE. (After Sachs.) 



Fig. 43. — Germinating 

 seed of cabbage : b^ 

 axis ; r, «', the two 

 cotyledons, which 

 have risen above the 

 :,.oil, the testa a not 

 being yet completely 

 thrown off. 



possible varies with different plants, but it may be stated gene- 

 rally as being between 5"" or 6° C. and 40° C. 



Either the roots at once lengthen and grow out through the 

 micropyle, or, which is more often the case, the lower part of 

 the cotyledon, known as the hypocotyledonary portion of the 

 stem, becomes elongated, pushing the end of the root before 

 it out of the seed. 



