328 
conspicuous feature, sufficient to identify the plant at a glance, is the 
inflation at the middle of each petiole, forming a sort of elliptical 
bladder, which on the larger leaves is an inch long by half an inch 
in diameter. The bladders are entirely closed, not hollow, but of 
the saine cellular, spongy texture as the petiole, and we suppose their 
purpose must be to assist in sustaining above the water the somewhat 
heavy clustered foliage. They form in fact a cordon of dife-preserv- 
ers about the central flowering parts. a a 
The flowers (June-July) are solitary, short-peduncled, axillary, 
small and white; petals, calyx lobes and stamens, four, the latter 
inserted with the petals on a disk crowning the ovary; stigma, one, 
capitate ; ovary semi-inferior, embraced by the adnate calyx tube, 
which rapidly enlarges in fruit to a turbinate, bony nut, nearly two 
inches long, one-celled and one-seeded from arrest } and from the 
calyx lobes are developed four sharp, spreading horns or spines, 
somewhat recurved, and often one-third of an inch long. ‘The seed 
is mealy and edible, resembling the chestnut. 
From the nut the plant is in Germany popularly called Schwim- 
mende Wassernuss—Swimming Water-nut-—-which is so apt that it 
might well bear here the same popular name, rather than that.of the 
“European Water Caltrop ” by which it has been sometimes called. 
However introduced, it bids fair to stay, and its gradual extension 
southwards may be looked for. Pi Be 
§$ 336. Gray’s Botanical Text Book.—In our notice of this work 
in the’ June No. there were some obvious typographical errors, p. 
318, 1. 4, “‘ Diplosteminous ” for Diplostemonous ; p. 319, about the 
middle “ Brown” for Braun ; and on p. 320, last line but one of third 
paragraph, “it is entitled” where “it” should be omitted, and also 
the comma after “ views,” in the next paragraph but one; and in the 
final line for “levaes” read leaves. But the chief error was the omis- 
sion of some words in a sentence near the beginning of page 318. 
The sentence should read: In the doctrine of the flower, Chap. VL, 
it is stated that “extended observation leads to the conclusion that 
the typical flower in nature has two series of stamens, as it has two 
series in the perianth,” or is Diplostemonous, the stamen circles alter- 
nating respectively with calyx and corolla. 
The more we read this admirable work, the more we are impressed | 
with its depth and its clearness. We embrace this opportunity to 
add the following exposition of the place of species in classification, 
as, perhaps, a necessary complement to our notice. 
“Species is taken as the unit in zoological and_ botanical classifi- 
cation.” .-. . “The aim of systematic natural history is to 
express their [species] relationship to each other. The whole ground 
in nature for the classification of species is the obvious fact that spe- 
cies resemble or differ from each other unequally and in extremely 
various degrees. If this were not so, if related species differed from 
one another by a constant quantity, so that, when arranged accord- 
ing to their resemblances, the first differed from the second about as 
much as the second from the third, and the third from the fourth, 
and so on,—or if the species blended as do the colors of the rainbow, . 
