in several distinct races of vascular Plants . 271 
what is imaginary for reality. This evil has been experienced 
in a particular manner in our inquiries into the nature of living 
and organised bodies, in which there is so much obscurity, and 
so much difficulty. The organs of animals have, indeed, been 
dissected and examined from very early times ; and more espe- 
cially, since the revival of learning in Europe. But our ac- 
quaintance with the structure of plants is of comparatively mo- 
dern date ; and is necessarily more imperfect, from their organs 
being less palpable than those of animals in general. In both, 
however, the obscurity and difficulty of the subject has afforded 
the usual scope for conjecture. Analogies have been assumed, 
on the slightest seeming resemblance of functions. Phenomena 
have been attempted to be explained, by reference to other phe- 
nomena imperfectly observed, and therefore imperfectly com- 
prehended in beings possessing little in common but the proper- 
ties of life and organisation, although in every other respect 
constituted on a distinct plan. Thus, since the discovery of the 
circulation of the blood by the acute genius of Harvey, a corre- 
sponding circulation of the sap in plants has been, contrary to 
the principles of just induction, first imagined, and then support- 
ed by argument ; and an arterial, venous, and lymphatic system 
of vessels has been, on very slight evidence, attributed to plants. 
Again, since the clear demonstration of the sexes of plants, by the 
celebrated Linnseus and his followers, terms have been borrowed 
from the appendages of the ovum of animals, and applied to those 
of the seed-vessels of plants, without due proof of the correctness 
of the analogy, and, therefore, with manifest injury to the unravel- 
ling of the truth. But, if it should be argued, that the fact of the 
existence of a sexual system in plants, is in itself a proof of the 
justness of such analogy, it may confidently be replied, that the 
existence of some truth in the analogy from which terms are 
frequently derived, has been one of the most usual means, first, 
of the reception, and, eventually, of the establishing of error. 
Analogy, of itself, is one of the most useful of all monitors in the 
study of truth : It affords the most important suggestions to the 
mind ; but these must be submitted to the ordeal of experiment, 
and patient observation, otherwise we shall be perpetually mis- 
led. It is not only unsafe, then, to draw conclusions from the 
laws of the animal economy, and to apply such conclusions to 
2 
