1875.] Notices of Books. 379 
can take its place as a manual of vegetable morphology and 
physiology. The translators well deserve the thanks of all 
friends of the organic sciences for having placed this rich treasure 
within the reach of the English student. 
The chapters on the elementary constituents of the food of 
plants ; on assimilation and metastasis (stoffwechsel); on the 
respiration of plants; and on the action of temperature, light, 
electricity, and gravitation upon vegetation, are most excellent, 
and may be consulted with advantage by the physicist and the 
chemist, as well as by the botanist. 
The last chapter is devoted to that difficult but fascinating 
topic, the origin of species. It may be interesting to learn what 
are the views of so eminent an investigator as Prof. Sachs upon 
this crucial question. He declares that—‘‘ The scientific basis 
for the theory of descent rests in the fact that it alone is able to 
explain in a simple manner all the mutual relationships of plants 
to one another, to the animal kingdom, and to the facts of geology 
and paleontology, their distribution at different times over the sur- 
face of the earth, &c, ; since it requires no other hypothesis than 
descent with variation and the continued struggle for existence 
which permits those forms only to persist that are endowed with 
sufficiently useful properties, the others perishing sooner or later. 
But both these hypotheses are supported by an infinite number 
of facts. The theory of descent involves only one hypothesis 
which is not directly demonstrated by facts, namely, that the 
amount of variation may increase to any given extent in a suffi- 
ciently long time. But since the theory which involves this 
hypothesis is sufficient to explain the facts of morphology and 
adaptation, and since these are explained by no other scientific 
theory, we are justified in making this assumption.” 
The Transit of Venus. By GreorGe Forses, B.A. (‘‘ Nature ” 
Series.) London and New York: Macmillan and Co. 
Tue work before us is based upon a paper originally read before 
the Philosophical Society of Glasgow, and subsequently pub- 
lished in ‘‘ Nature.” There is scarcely any point connected 
with the entire question but receives a lucid explanation. The 
reader will learn what is a transit of Venus, the reason of its 
rarity, and its value in enabling us to calculate the true distance 
of the earth from the sun. We also find an explanation of the 
term ‘ parallax,’—not, of course, of the gentleman who assumes 
that name,—and a brief notice of other methods by which the 
sun’s distance may be determined, such as the parallax of Mars 
when nearest the earth, which occurs every fifteen years; the 
method founded on the velocity of light and the procedure of 
Leverrier, materials for which are gradually accumulating. The 
