ON THE TORPIDITY OF PLANTS. 151 



and explaiiii and, in its changed condition, descends down the stem, 

 depositing additional layers of woody fibre, and a sufficient quantity 

 of nutritious material, so as to protect the individual plant fiom the 

 depressing and deadening influence of the winter *s blast. This is the 

 precise condition in which we find the vegetable kingdom at the present 

 lime, in a state of repose, not of death. Death has been defined to be, 

 that condition in which all resistance on the part of the vital force 

 entirely ceases ; therefore, so long as this condition is not established, 

 the living tissue continues to oflTer resistance. 



Certain animals which cease to eat on the setting in of winter, 

 such as the squirrel, the bat, the snake, the frog, the pnail, and 

 numerous species of insects, continue to live in a sluggish and nearly 

 motionless state, which state is very different from sleep in several 

 circumstances, particularly in the very slow and scarcely observable 

 circulation of the blood and of breathing, the rapidity of which is not 

 very greatly affected during ordinary sleep. It is on this account 

 that the terms torpidity or torpid should rather be chosen in prefer- 

 ence to the terms donnancy and donnant. Such animals are found 

 previous to winter to become unusually fat, as indeed is the case 

 with most other animals, owing, in part, to the loss of substance, 

 becoming less as perspiration diminishes with the increase of cold. 



Now plants, during winter, seem to be in circumstances very similar 

 to those of torpid animals, the circulation of the sap like that of the 

 blood, and the changes effected by air and light, like the process of 

 breathing, being scarcely, if at all, observable. With respect to the 

 increase of fat, it is said by De Caudolle and others, that a larger 

 proportion than usual of nutrient pulp accumulates in the root and 

 pulp wood, or alburnum. 



Thus far, then, I think I have succeeded in explaining the nature 

 of the peculiar condition, or torpidity, of plants during the winter 

 season. Let us now proceed to enquire into the causes which produce 

 this condition. 



It is of importance here to remark, the almost universal tendency 

 there is in animated nature to periodicity. The most casual observer 

 of nature cannot have failed to remark this tendency ; as is evidenced 

 in the casting off the superficial layer of the covering of insects, the 

 crust of the crab, the scales of the fish, the plumage of the bird, the 

 hair and other epidermic appendages in the different races of quad- 



