42 Microscopic Observations, 



as we think, termed spines, which, physiologically considered, 

 are abortive branches, needing only peculiar circumstances to 

 call them into a gemmiferous and leafy habit. Here then the 

 character of pubescence is changed or modified, from delicate 

 vascular structures, to rigid and indurated forms. 



The leaves of aquatic plants are also destitute of such organs. 

 The leaves of amphibious vegetables ai-e smooth when un- 

 der water, but of a different form and texture when emersed. 

 Several species of iJanunculi have sets of foliar appendages, 

 with different degiees of pubescence. 



From these and similar considerations we should conceive that 

 a system of pubescence on different plants might afford impor- 

 tant data in the methods of studying their habits, and employing 

 the results of such study to their certain and successful cultiva- 

 tion. Thus, if it be true as has been conjectured, that the office 

 of the hairs, which constitute the pubescence, be to prevent a 

 too rapid evaporation from the stomata of the leaves, and to pro- 

 tect their surface from too great heat or moisture, then where 

 these natural provisions are artificially effected, should we not 

 notice some change in their general economy? Or, were these 

 minute organs intended to facilitate evaporation by creating a 

 greater surface without extending the amplitude or circumference 

 of the leaf, ought not a change in their nutrition effect a corres- 

 ponding change in their economy? To what end are the young 

 leaves so abundantly provided, which on maturation lose such 

 a provision? Or why, as others expand, (for instance, those of 

 the horse-chestnut,) they part with the superfluous covering, 

 so palpably apparent in their primary expansion? In these two 

 cases there would seem to be a temporary provision against the 

 effect of cold in the critical period of their vernation. 



But the structure of the pubescence, as well as its presence, 

 claims our attention and admiration. Perhaps there are few sub- 

 jects for the microscope of greater interest, so far as real beauty 

 and elegance of form is concerned, than may be found in the 

 pilose clothing of leaves of different plants. The more aston- 

 ishing discoveries of physiological botany which this instrument, 

 in the skilful hands of the patient investigator, have made and 

 given to the world, require a peculiar genius and talent, with 

 great nicety of operation, to trace. The difficulty of procuring 

 proper instruments, and the expense of accurate ones, have ex- 

 cluded these deeply interesting studies from many an inquirer 

 into the mysteries of organized matter. Nor are experimenters 

 themselves mutually agreed respecting various minute but impor- 

 tant organs, as their form, function or even existence. Not im- 

 perceptible to unaided vision, as are these just mentioned, the 

 pubescence, with ordinary instruments of considerable power, 

 will display diversity and beauty combined. A bouquet from 

 the green-house, the few plants of our own cultivation in the 



