6 INTRODUCTION. 



principal use of the expanded leaves is to elaborate 

 nutritious materials for the formation of the suc- 

 ceeding next year's bulb ; or, that the substance 

 of the old is somehow transferred into the new 

 one. This idea is at least questionable ; because 

 the bulb of the tulip lying in a drawer, where no 

 developement or expansion of leaves can take 

 place, will, notwithstanding, put forth its new 

 offset bulbs, with no other assistance than what 

 its feeble fibres, produced at the same time, can 

 collect in this unnatural situation ; and if it be 

 intended to produce a numerous progeny of offsets, 

 half the old bulb (the upper half) is cut off before 

 it is planted, to produce this effect. Young 

 tubers, as the potatoe, are produced without the 

 assistance of leaves. True it is, that when a 

 part, or the whole organisation of a plant is in 

 motion, there is a reciprocity of assistance from 

 any one to all the others ; but this does not 

 appear to be the peculiar office of the leaves more 

 than it is that of the roots, if indeed so much. 

 Checking the oviparous principle will stimulate 

 the viviparous, or vice versa. But, except re- 



