206 INTERCELLULAR SPACES. 



the material for its formation, must be derived from the cells, which closely of 

 immediately surround the space. Where it is possible, as e. g. in the case of the 

 above-mentioned resinous secretion around the reservoirs, to prove its presence in the 

 cell-contents, it may be assumed that it passes as such from the cells into the reser- 

 voirs, of course not by filtration in great masses, but, as Miiller assumes, by diffusion 

 through the membranes in successive small quantities. This view is supported by the 

 fact that, according to Miiller in the Coniferae, and Sachs and van Tieghem in the 

 roots of Compositae, the intercellular spaces are first present without the characteristic 

 secretion, and that this first appears in them at a later stage. 



On the other hand there occur, as above stated, cases where the secretion is also 

 of a resinous nature, but is not proved to occur as such in the cell-contents in the 

 vicinity of the reservoir. Further, Sanio has recently expressly stated that the resin- 

 passages of Pinus are filled with the secretion even from the time of their first origin ^ 

 So far as my investigations extend, the young stage of the passages of the root of 

 Compositse, when the secretion is absent, is at best very transitory: the secretion 

 appears very early, and may be easily overlooked in the narrow young passages : it 

 may be really absent, especially in transverse sections, since it may have flowed out. 



Since, in the dermal glands of the epidermis, secretions, which are in every re- 

 spect similar to those under consideration, are often to be first observed anatomically 

 as constituents of the cell-wall, and further since the intra-mural glands (p. 96), 

 when regarded purely histologically, are merely a special case of schizogenetic 

 secretory cavities in the epidermis, the question arises, whether in all cases the 

 secretions of schizogenetic reservoirs are not to be regarded as constituents of the 

 cell-wall. The actual observations supporting this view are of at least equal weight 

 to those supporting the other, while none of the latter exclude the correctness of the 

 former view. 



All secretory passages, with the exception of the few named on p. 205, are of 

 schizogenetic origin ; of these however the mucilage-containing passages in Canna 

 must be more exactly investigated ; also besides those cavities already mentioned in 

 Lysimachia, Myrsinese, and Oxalis, those which take the place of passages in many 

 short leaves of Conifers deserve further attention. 



Further descriptions in detail of the secretory passages must so often have reference 

 to their arrangement, that, to avoid repetition, they must be given subsequently in 

 Chap. XIII. 



Here those which are found in species of Mamillaria will alone be described. In the 

 literature I find it only briefly mentioned that these plants have latex (De Candolle), 

 which is contained in passages (Unger). Investigation shows, firstly, that the Mamillarias 

 are entirely without those mucilage-sacs (p. 143) which occur in the allied genera. I also 

 find no trace of intercellular secretory reservoirs in small species, as M. glochidiata and 

 the like; and in an unnamed, very robust species. On the contrary, M. angularis, Hystrix, 

 and Zuccariniana have a complex system of branched passages. These are limited, as seen 

 in transverse section, by one 4-5 celled layer, or by two, or even three concentric layers 

 of delicate cells, flattened tangentially to the passage : the width of the passages is about 

 equal to that of one large cell of the parenchyma. They contain a thick, uniformly finely- 

 granular, colourless juice, which emerges on section in large white drops, and hardens 



' /. c. p. lOI. 



