REVIEWS. 
413 
Lis dimorphic and trimorphic plants proved them to behave very much after 
the fashion of hybrids between distinct species ; and this leads him to discuss 
the question of hybrids at some length, and more especially the hybrids of 
the species of Primula , which are numerous even in a state of nature. He 
also notices the peculiarities of monoecious, dioecious, and polygamous 
plants, of which he maintains that, “ as the separation of the sexes would 
have been injurious, had not pollen been already transported habitually by 
insects or by the wind from flower to flower, we may assume that the 
process of separation did not commence, and was not completed, for the sake 
of the advantages to be gained by cross-fertilization. The sole motive for 
the separation of the sexes,” he adds, “ which occurs to me is, that the pro- 
duction of a great number of seeds might become superfluous to a plant 
under changed conditions of life ; and it might then be highly beneficial to 
it that the same flower, or the same individual, should not have its vital 
powers taxed, under the struggle for life to which all organisms are sub- 
jected, by producing both pollen and seeds.” This explanation is hardly 
satisfactory, and does not apply at all to monoecious plants. Among 
polygamous plants Mr. Darwin distinguishes a sub-class which he calls 
il gyno-dioecious,” in which the unisexual flowers are all females, and he 
says that they yield a much larger supply of seed than they would have 
done if they had 'all remained hermaphrodites — in other words, fewer 
stamens than would exist in the flowers if all were hermaphrodite are 
capable of producing sufficient pollen for all their pistils. This is pro- 
bably true also of the ordinary monoecious and dioecious plants, but still we 
cannot see where the necessary saving of material or powers comes in with 
sufficient force to account for phenomena of such importance. It must be 
borne in mind, however, that these suggestions of Mr. Darwin’s are merely 
tentative, and that we have still much to learn before the “ why and 
wherefore ” of all these things is laid open to our view. 
Nevertheless by works such as this, chiefly inspired by the new spirit 
thrown into natural-history research by the Darwinistic publications, we 
cannot doubt that progress is being made in the right direction. Any 
attempt at the explanation of phenomena is a step towards the truth ; if it 
justifies itself it is absolutely an advance ; if its justification be difficult, 
partial, or even impossible, the researches necessary for testing its value 
must in any case lead to valuable results. Even the steps taken apparently 
on the most indisputable grounds may open questions that it is very diffi- 
cult to answer. Thus, to take the case of the Primulas, many species of 
which, as we have seen, seem to be specially organized so as to render 
cross-fertilization a necessity, we find, side by side with the “ heterostyled ” 
species, others which are “ homostyled ; ” and it is hard to see, from the 
conditions of existence of the plants, why one set should be so peculiarly 
modified, and the other set left in what we may call a normal condition. 
So also with the monoecious and dioecious plants in groups the flowers 
of which are normally hermaphrodite. These and many other matters 
of doubt, which may easily occur to the mind in studying Mr. Darwin’s 
•descriptions of the different forms of flowers, furnish objects of study 
which we recommend to the attention of our readers ; they are points not 
very difficult of investigation under the guidance to be obtained from 
