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POPULAR SCIENCE REVIEW. 
ence between these plants, as we have depicted it in the Ann. 
Nat. Hist.” for December 1863. Again, compare the spores, the 
tissue-cells of the fronds and involucres of Hymenophyllum 
Tunbridgense and H. Wilsoni, when they will be found regu- 
larly smaller in the former than in the latter fern, as shown by 
our engravings in Dr. Seemann's ‘‘Journal of Botany,” for 
October 1863. And yet these two plants are often described 
as mere varieties of one species. 
But still more notable illustrations are found in those beau- 
tiful organisms, the raphides and their cells, so fully described 
in the “ Popular Science Eeview,” for October 1865, that we 
will now only add another remarkable and unexpected proof of 
the validity of the views there advanced. Premising that the 
rapbidian character is signally fundamental and universal in 
certain plants, e.g, Onagraceae, as it is present in the seed- 
leaves, and pervades the greatest part of the tissues from the 
cradle to the grave of the species, we had long searched in vain 
for the exception of an ex-raphidian plant in this order, when 
at last a supposed one was found in Montinia. But further 
inquiry led to the discovery that this genus, though placed by 
Lindley and other eminent botanists under the order Onagraceae, 
does not truly belong to it, but rather to the Saxifrages, with 
which its cell-structure better agrees. And thus a seeming 
exception became a strong proof of the rule. 
And this is the only instance in which a plant not familiar 
to English botanists has been mentioned in this paper. For 
the examples of microscopical structure have been purposely 
confined to such as, though not to be found in the books of 
systematic botany, are abundant in the book of Nature, and 
may be easily verified in the most familiar plants, with the aid 
only of an achromatic object-glass of half an inch focal length. 
The pursuit might prove at once delightful and instructive, and 
could hardly fail to produce useful results; with the conviction, 
too, that specific details of the pollen and other cells must form 
an interesting and important part of any future and truthful 
description of the natural characters of our flora. 
