RESISTANCE TO HEAT, COLD AND DRYNESS 89 



importaut that seeds, wliicli are carried in tliis manner, shall 

 be of such character as not to be easily injured by long sub- 

 mergence in water, and this is especially true of those seeds 

 which are carried by salt water. The cocoanut is a striking 

 example of a large floating seed which frequently is carried 

 on the salt water. The vegetation of the volcanic and coral 



Fig. 65. — Devices for seed distribution. 



islands of the sea frequently owes its origin to seeds of this 

 type. 



Resistance to Heat, Cold and Dryness. — The seeds of many 

 plants are also, resistant to exti'cme drying and to extreme heat 

 and cold. The seeds of some plants will lie in the soil for 

 years waiting nntil the conditions are favorable for their germin- 

 ation, while the seeds of other plants will perish in a few 

 weeks or months, even when kept under the most favorable 

 conditions. 



