NEW PUBLICATIONS. 89 



division to anotlier. As we meet with more lowly differentiated types, it 

 becomes, in fact, more and more impossible to discuss properly, apart 

 from each other, structure aiul function. 



The introductory remarks deal with the distinctions between plants 

 and animals. First and foremost is, of course, their fundamental reUition 

 to the inorganic world. The most philosophical plan is to show how all 

 other differences can be made to How from this one. Too much stress is 

 perliaps laid on the absence of nitrogen from the permanent parts of 

 plants ; they are as incapable as animals of existing without it, and, in- 

 deed, it is obvious that if they were devoid of nitrogen, animals must be 

 so also, as all animal nitrogen is derived ultimately from the plant world. 

 Tiie greater proportion of nitrogen required by animals seems to depend 

 on their greater activity. There is no activity without chemical change in 

 the tissues of the living organism, and as all organic nitrogenous com- 

 pounds are unstable, it is not unreasonable, with Mr. Herbert Spencer, to 

 correlate the mutability of these compounds with the presence of nitrogen. 

 Plants are in the main passive, not active ; hence the presence of any 

 large proportion of nitrogen in them would be useless. As we descend 

 in the animal world, we are not surprised to find indications of plant 

 peculiarities ; hence, in some Molluscoida, we have a substance not very 

 different from cellulose, and fiually, in the Racliolaria, actual starch, indis- 

 tinguishable from that of vegetable origin.* 



It seems to be an accepted principle to restrict botanical text-books to 

 recent plants, and to say as little as possible about fossil botany. In the 

 present volume the subject is altogether omitted. This seems a matter 

 for regret, because in the case of any particular group, the great end in 

 view should always be to reach the most generalized conception of its 

 structure, and fossil plants may supply in part or even wholly the key to 

 this. There is a general impression, for example, that acrogenous plants 

 only grow at their summits ; yet the gradual elongation of the leaf-scars 

 and their separation from one another as we proceed from the newer to 

 the older parts of the stem, prove that in the Lepidodeiidrons, as in 

 existing tree-ferns, growth never absolutely ceased in a longitudinal di- 

 rection at any part of the axis ; again, in Lepldudendron, the vascular 

 tissue of the stem was not at first produced to its full extent, but was 

 continually added to from a Cambium layer, an arrangement of which, 

 among allied plants, hoeles is the only existing representative. No ac- 

 count, however, of the little-noticed structure of the corm of this cru-ious 

 plant is to be found in the present volume. The necessity, in any really- 

 general study of morphology, of taking into account both existing and 

 recent types of plants, is well illustrated by the structure of Beuneliitfs, a 

 genus of fossil Cycndere, which has been shown by Mr. Carruthersf to be- 

 long to an entirely new group of the Order, standing to some extent in the 

 same relation to other Cycads that Taxns does to other Coniferce. Besides 

 the possession of a trunk ovoid in outline, the woody cylinder is pierced 

 by large meshes for the passage of the whole of the fibro-vasrular buiulles 

 j)assing to each leaf, — an arrangement which can only find its parfllel in 

 the caudex of tree-ferns In all other Cycads a number of small bundles 

 perforate the woody cylinder separately to pass collectively into each 

 petiole ; and here, it must be observed, that in describing the structure 



* See 'Nature,' vol. ii. p. 178. 



t Trans. Linu. Soc. vol. xsvi. p. 695. 



