80 PEOPAGATIOSr OF PLANTS. 



of course, certain families of plants, the seeds of wMch 

 possess much greater tenacity to life than others, hut in 

 all, time is a weakening element. The seeds of Melons 

 and Cucumhers may be preserved in good condition for 

 grow bh from one to fifteen years, and even at the latter 

 age yield a fair proportion of plants, while the seeds 

 of the Onion, Carrot and Celery soon perish if kept 

 under the same conditions, few germinating after they 

 ore three or four years old. 



Then there are other kinds of seeds which require age 

 and long exposure to heat and moisture to soften their 

 horn-like covering, as in those of the Cratmgus, Mespilus, 

 Cornus, Halesia, Hex, and several species of the Eose ; 

 but in all of these, and others of like character, a few 

 weeks' exposure to a dry atmosphere will either destroy 

 vitality, or so harden the shell that the pores of the latter 

 will not open again to admit moisture to the kernel. 



It might readily be supposed that the natural sur- 

 roundings of vessels enclosing seeds would not only 

 afEord the best protection, but also insure the most favor- 

 able conditions for the prolongation and preservation of 

 their vitality, and while this is true in many instances, it 

 is quite the contrary in others. The pulp of the Apple, 

 Pear, Quince and similar fruits, if left to decay about the 

 seed, is almost certain to destroy it, from the chemical 

 changes which occur in the decomposition of what is 

 called the fruit, consquently to remove the seed by arti- 

 ficial means is assisting nature in its preservation. 



There are seeds which naturally begin to grow while 

 still attached to the fruit-stalk, not separating from the 

 parent plant until after germination and the production 

 of roots. The fruit of the Mangrove tree {Rhizophora 

 Mangle), of Southern Florida, is a well-known example of 

 this kind of seed. Then, again, there are other seeds 

 which will remain sound for many years if kept sealed up 

 in their natural and multiple integuments, as seen in 



