CRYPTOBIOTIC STAGES IN BIOLOGY 7 



In many seeds there may be inhibitors of germination found 

 in the fruit that covers the seed, or in the seed coating^^. As long 

 as these are present, no germination can take place. During 

 storage in the soil or other suitable environment, these inhibitors 

 may leach out slowly or may even be destroyed by micro- 

 organisms. Following their removal, germination can take 

 place in a normal manner. In a single batch of seeds, not all of 

 them will free themselves from the inhibitors at the same time. 

 The different individuals may germinate at various times over 

 a long period, thus helping to insure the propagation of the 

 species. Germination in some seeds is triggered by a periodic 

 change of temperature, that is, from storage at a low tempera- 

 ture to storage at a high or moderate one. In some cases, more 

 than one cycle of temperature change may be necessary. The 

 mechanism involved here, as it must be in many of the other 

 cases, must be biochemical, a temperature change being neces- 

 sary for the proper sequence of biochemical changes. Un- 

 fortunately, these phenomena are not understood, so that we do 

 not have even fragmentary knowledge of the mechanism. 



Some seeds, like those of the legumes, have a very hard 

 coating that is practically impervious to moisture and oxygen, 

 so that the seed embryo within the shell is kept in a state of an- 

 hydrobiosis, even though the environment outside the shell is 

 conductive to germination^-*. These seed shells have interesting 

 properties in that they will allow the moisture within the seed to 

 escape, preserving the embryo through dehydration, but will 

 not let water pass in the reverse direction. Such seeds can be 

 made to germinate quickly by mechanically or chemically 

 injuring the shell in order to let water in. In nature, such seeds 

 may depend upon the action of bacteria from the outside to 

 damage the coat, so that moisture can reach the embryo. 



BUDS 



The buds of plants usually remain dormant for a shorter or 

 longer period, and many never open up. Whether or not they 

 vegetate depends upon a number of conditions: such as favor- 



References p. 13 



