32 Principles of Plant Culture. 



subtracting the number that fail to sprout from the num- 

 ber put in, the per cent of vitality may be readily com- 

 puted. The cloths should be placed in boiling water a 

 few minutes before using them for a second test, to de- 

 stroy any spores or mycelia of mold with which they 

 may have become infected. 



40. The Time Required for Germination varies greatly 

 in different kinds of seeds. In lettuce seed, the tiny 

 white shoot often breaks through the seed-case within 

 twenty-four- hours from planting, while celery seed re- 

 quires several days to germinate to this extent. The 

 seeds of many plants will not germinate the same season 

 thej< are formed, even if planted under the most favor- 

 able conditions (163). 



Individual seeds of the same kind and of the same 

 sample often vary greatly in the time required for ger- 

 mination. Even in seeds that germinate soonest, as let- 

 tuce and radish, some individuals will not germinate 

 until several days after the majority have germinated. 

 Seeds of tobacco and purslane* sometimes continue to 

 germinate through several successive seasons. The rea- 

 sons for these variations are not known. 



SECTION III. THE PLANTLET 



By watching the germination of seeds, we may learn 

 some interesting facts. Viable seeds will usually germi- 

 nate freely on the surface of well-moistened soil or sand, 

 if we provide a damp atmosphere above them by cover- 

 ing with a bell-jar or otherwise, for light does-not hinder 

 germination. One of the interesting facts connected 

 with germination is, that the first shoot, called 



* Portulaca oleracea. 



