SPECIAL MORPHOLOGY : RIIIZOCARPE^E. 209 



fruit, which promises results in the highest degree interesting, is up to 

 this time a pium desiderium. The Rhizocarpecp have found no place 

 in Meyen's System (!). From what is known, and what I have myself 

 seen, this much follows, that there is no room at present for fictions of 

 blending together of organs and the like. On the other hand, from the 

 situation of most of these fruits (comparing them with the Lycopodiacece), 

 it is exceedingly probable that we have to do merely with a small 

 portion of a leaf, developed in such varied ways in its interior. But 

 this does not at all give a different import to the anthers and seed-buds 

 from that universally admitted for sexual plants ; and the fact that in the 

 Phanerogamia the anther only is formed from a leaf, the seed-bud pro- 

 bably only from a stem, is thus peculiar to this group, but by no means 

 an essential part of the conception of anther and seed-bud. To attach 

 in this way to every word an absolute definition, and not to use it to 

 express misty schemata of the imagination, is the only way to bring 

 security and progress into science, and to free it from the nauseous and 

 not merely fruitless, but terribly destructive, indiscriminate use of words 

 by which no two persons understand the same thing. The process of 

 development appears to be especially peculiar in the seed-buds of Pilu- 

 laria. In some earlier conditions of these I found the seed-sacs filled 

 partly with delicate transparent globular cells, and partly with groups of 

 four tetraedrally-united cells; one of the latter gradually underwent 

 considerable expansion, but especially in one group which occupied 

 exactly the centre of the seed-sac, so that this soon filled the greater part 

 of the space, and could no longer be mistaken for anything else than the 

 future embryo-sac. All the rest of the cellular tissue appeared to be 

 subsequently converted into the coriaceous coat of the ernbryo-sac, and 

 the gelatinous one of the seed-bud ; but my observations on this point 

 are imperfect. 



I have thus largely treated of the Rhizocarpece, only because in no 

 previous publications have the so desirable completeness and accuracy 

 been attained, and in the belief that I was able to furnish some not un- 

 important contributions ; besides, also, that their position, as a decided 

 intermediate link between the Phanerogamia and Cryptogamia, makes 

 an accurate knowledge of them in the highest degree important and 

 fruitful. 



118. The structure of the Rhizocarpea is, on the whole, very 

 simple. The stem consists of a central vascular bundle, with some 

 spiral vessels, and a bark in which run a circle of large air-canals, 

 covered on the outer side by a simple layer of cells (in Salvinia), 

 or by several layers (in Pilularia and Marsilea). The septa of the 

 air-passages of the last consist of elegant stellate cells ; in both 

 Pilularia and Marsilea the vascular bundle is enclosed by a simple 

 layer of elongated parenchymatous cells with brownish walls. The 

 leaf of Pilularia, and the petiole of Marsilea, are formed exactly in 

 the same way as the stem of Salvinia, only they are, in addition, 

 covered by an epidermis with stomates. The blade of the leaf of 



contents. C, Seed-sac. D, The same in longitudinal section : a, seed-sac ; ft, cori- 

 aceous coat of the seed -bud ; c, three-lobed coat of the seed-bud surrounding the 

 nucleus ; d, embryo-sac ; e, the place where the pedicle of the seed-sac was attached, 

 E, Apex of the seed-bud, seen from above. 



