166 MOKPHOLOGY. 



as we have obtained in the case of the Phanerogamia.* We cannot, there- 

 fore, as yet express a common law for the peculiar relation existing between 

 leaves and propagating cells, owing to the difficulties which have hitherto 

 presented themselves in Mosses and Liverworts. For the rest, it appears 

 tolerably easy to bring this law into harmony with the nature of the/stem 

 and leaf. The latter alone contains, especially, the perfect living cells, in 

 them alone the nutriment that has been taken up is specially concentrated ; 

 consequently it is peculiarly here that a sufficient quantity of assimilated 

 matter can be formed to bring about an organic crystallisation, cellular 

 formation ; and it is only in these cells that, under the circumstances of 

 the quantitatively limited growth of the leaf, such an amount of assimi- 

 lated matter can be accumulated as to bring them into a position to begin 

 an independent process of vegetation. 



Here, for the first time, we meet with a special formation of organs, 

 since a morphological distinction is produced in the process of develop- 

 ment, and we find, on the one side, a quantitatively unlimited stem or 

 axial part, and, on the other, a limited lateral part; that is to say, in the 

 former the axis or stem, in the latter the leaf. To this we may add 

 in the higher groups, another separation of the stem into stem in a more 

 limited sense of the word, and into root, depending upon the distinction 

 between the opposite directions of the unlimited and continuous de- 

 velopment of the stem part, or axis. 



95. The GymnosporcR are essentially distinguished, in an 

 anatomical point of view, by the formation of vascular bundles 

 in the stem or in the leaves. The individual development of the 

 separate cells belongs also to a very far higher stage, since, with 

 the exception of the Mosses, we everywhere clearly distinguish 

 spiral thickening layers. Finally, there is no group in which we 

 do not meet, in the separate species or parts of the plants, with a 

 perfectly developed epidermis with stomates. 



I have already remarked above ( 26.), that I see no reason why 

 we should not apply the term " vascular bundle " to the circle of elon- 

 gated cells in the stem of the Mosses and Liverworts, since it has a 

 similar position and exercises similar functions, if we compare it with 

 the vascular bundles of the Phanerogamia without the so-called spiral 

 vessels, as, for instance, in the Ceratophyllum, which has likewise a simi- 

 lar anatomical structure. The bundles of elongated cells establish a 

 striking anatomical distinction between Gymnosporce and Angiosporce, 

 nothing bearing any resemblance to them appearing in the latter. The 

 considerable development of the spiral thickening layers forms a no less 

 special difference between these two groups, and it is remarkable that 

 there is not a trace of this formation to be met with in Mosses. 



A. ASEXUAL PLANTS (PL agama). 



96. The Ayamce present three stages of development : 

 1. The Liverworts form the transition from the Angiosporce to the 



* What requires to be essentially specified concerning stem and leaf must be deferred 

 till we treat of the Phanerogamia, and then our remarks on the subject will be perfectly 

 applicable to the Agamce, except in the cases where previous notices of the latter make 

 limitations necessary. 



