164 -D r . Smith’s Obfervatiotu on the 
informed me, that he is ftrongly of this opinion ; and that he 
fhould not defpair, by throwing acid or other Simulating in- 
jections into the veffels of fome plants, of feeing with a mi- 
crofcope at once the propulfion of the fap, and the contractions 
by which it is performed. He urged me, with that amiable 
enthuliafm for which he is remarkable, to purfue the inquiry. 
Whether I do fo or not, I think the idea too interefting to be 
kept to myfelf, and fhould be glad to fee it realized by any 
one who has time and abilities for fuch inveftigations, who has 
accuracy and coolnefs in making his experiments, as well as 
fidelity and impartiality in recording them. 
I cannot conclude this Paper without taking notice of ano- 
ther very curious property which vegetables feem to poflefs in 
common with animals, although certainly in a very inferior 
degree : I mean, that property, to ufe the words of Mr. Hun- 
ter, who has ftudied this principle to a vaft extent in the ani- 
mal ceconomy, by which their conSitution is capable only of a 
certain degree of aCtion confidently with health ; when that 
degree is exceeded, difeafe or death is the confequence. It is 
only by the help of this principle that I can explain why many 
plants refiS a great degree of cold for feveral winters before 
flowering ; but, after that critical event, they perifh at the firft 
approach of cold, and can by no art be preferved fo as to fur- 
vive the winter. But a more curious inftance is that mentioned 
by Linnaeus, without an explanation, in his Diflertation on 
the Sexes of Plants, of the long duration of the piftilla in the 
female hemp, while unexpofed to the male pollen; whereas 
thofe to which the pollen had accefs immediately faded and 
withered away. In this cafe, 1 cannot help thinking, that 
in thofe piftilla on which the pollen had adled, and which con- 
fequently had performed the function for which they were 
4 defignedj 
