962 The American Naturalist. [November, 
may be both vegetable and animal, or may be first the one and 
then the other.” 
So numerous have been the vain attempts to find some 
character of universal diagnostic value that it seems rash in- 
deed to make another trial. But, in case of failure, no harm 
will be done, even if no advance has been made. 
In all attempts, so far as they have come to my notice, the 
characters selected to distinguish the two kingdoms have been 
physiological, and not structural. Yet, in the classification of 
plants among themselves, or of animals among themselves, 
the characters of acknowledged value are drawn from structure, 
and physiological distinctions are only considered when the 
organisms are very minute or simple, like the bacteria and 
yeasts, or for some other exceptional reason. It seems, there- 
fore, highly illogical to accept a purely physiological character 
as fundamental for separating the two kingdoms. 
On this ground we would discard Linnzeus’ classification :* 
Lapides crescunt, vegetabilia crescunt et vivunt, animalia . 
crescunt, vivunt et sentient; and that of Heckel® who accords 
the chlorophyll function to plants and not to animals; and 
that of Sedgwick and Wilson” who find the sole characteristic 
of animals to be dependence upon proteid food ; and also that 
of Dangeard® and Minot,’ who distinguish the two kingdoms 
by the manner in which the food, or food material, is taken 
into the organism. There are also characters, for which I need 
cite no authority, that were advocated at different times in the 
past, which have since been discarded for lack of universality, 
such as a carbon dioxide respiration in plants and an oxygen 
respiration in animals, that plants exclusively convert in- 
organic matter into organic matter, that plants alone produce 
chlorophyll, or cellulose, or starch, etc. 
5 Philosophia botanica, ed. 4, 1 
ê Systematische Phyl. genie ve neh te und Pflanzen, 1894; abs, in Science, 
i, 1895, p 272. 
1 Biology, 1886, p. 167. 
8 Ann, des sci. nat., 7th ser., Bot. T. V.; Comp. rend., 1887; Le Botaniste, 
1895, p. 188. 
? Science, i, 1895, p. 311. 
