THE REST-PERIOD OF SEEDS 419 



etc., will, if kept in a protected position, maintain their vitality 

 for from three to six months. If, however, there is an excess 

 of atmospheric moisture on the one hand, or drought on the 

 other, the time is much shortened. Some seeds of palms, he 

 adds, like those of Maurifia, will not keep more than a week 

 or two. Tropical seeds in general, according to Mr Hart, are 

 as a rule possessed of a very fugitive vitality. To keep seeds 

 in stock is, he says, an absurdity, and the only practical rule 

 is to clean partially and sow at once for the best success. 



It is thus evident that the rest-period must be often a 

 transient feature with the seeds of many plants. Not only is 

 this the case, but there are many plants, as already indicated, 

 where the seeds experience after-ripening, the immature embryo Theafter- 

 of the resting seed continuing to grow up to the time of ger- ^^^ ng 

 mination. Such seeds, as Ewart observes, have apparently no 

 rest-period. Amongst examples given by Goebel and others 

 are those of Anemone^ Corydalis, Crinum, Ranunculus Ficaria, 

 Eranthis hiemalis, Gnetum gnemon^ Utricularia, etc. ; but the same 

 may be inferred of numbers of other plants where the embryo 

 is immature or but slightly differentiated, such as Cuscuta^ 

 Qrobanche, Monotropa, Balanophore<z, etc., named by Kerner, and 

 Stylidium, Gagea^ and Erythronium, suggested by Ewart. 



But in this matter we can make a much wider cast with 

 our net. After-ripening must often be counted upon by the 

 agriculturist and the gardener. They know that certain seeds 

 cannot be forced. It is the experience of the gardener, says 

 Kerner, that many seeds have to mellow or ripen before 

 germination ; and he reminds us that in many cases seeds 

 germinate in the spring under apparently much less favourable 

 conditions of temperature and moisture than they enjoyed in 

 the late summer and autumn of the previous year, when they 

 were first detached from the plant. 



There is another familiar feature in connection with resting The varying 

 seeds which has been already implied, namely, the great varia- development 



tion in the degree of development attained by the embryo 



when entering the resting stage. In some the embryo is in ing seed 



