24 Transactions. 



an apical meristem is set apart from which a plerome strand arises, and 

 that this strand of tissue functions solely in the transportation of food 

 from the parent prothallus up to the growing apex of the shoot. There 

 is nothing to indicate a possible root-rudiment. The haustorial processes 

 are many in number, and no one of them more than any other could be 

 suspected of being such a degenerate or arrested root organ. There is also 

 the broad zone of meristematic cells lying between these processes and 

 the axis of the plant. Of what nature is this ? Only a series of embryos 

 more complete than that described in this paper can indicate at all satis- 

 factorily the first differentiation of the embryo into shoot and foot, and 

 whether or not a root-rudiment is present. If the shoot develops from 

 the lower half of the embryo, then there would necessarily have to be a 

 curvature in the forward growth of that region (as in the Lycopodium 

 embryo) so as to allow the shoot to emerge, as it certainly does, at the apex 

 of the prothallial eminence on which the embryo has been developing. The 

 segmentation in the upper primary half of my embryos is certainly not as 

 clear and regular as it is in the epibasal region of the Equisetum embryo, 

 which there gives rise to the shoot-axis ; but, on the other hand, it does 

 not suggest the Lycopod suspensor. My own opinion, based upon the 

 study of the embryos described in this paper and of the young plantlets. 

 is that the shoot arises from the upper region (i.e., nearest the arche- 

 gonial neck), and that the lower half gives rise only to the foot, the surface 

 cells of the latter growing out into the peculiar haustorial processes. I see 

 nothing to indicate a root. There is no cotyledon, the first leaves being 

 formed at a very late stage as mere scales from the apical cell of the 

 shoot after the latter has emerged from the surface of the humus and has 

 changed its character from a rhizome to a green aerial stem. 



A still younger plantlet than that just described is shown in median 

 longitudinal section in figs. 61 and 62. The shoot took the form of a 

 globular protuberance from the surface of the prothallus. Sections through 

 the foot showed that the characteristic haustorial outgrowths were only 

 in the first stages of formation. The spherical shoot showed at one point 

 a slightly conical projection, which in section was seen to be composed of 

 meristematic tissue. This was obviously the actual apex of the shoot, but 

 no vascular strand had as yet arisen from it. The main portion of the 

 shoot consisted of large uniform cells in which the coils of the mycorhiza 

 were already established. The apical region consisted of smaller regularly 

 arranged cells, free from fungus, and showing conspicuous nuclei. I was 

 not able to distinguish whether or not there was a single, apical cell 

 present. Fig. 61 shows the plant as a whole in median longitudinal 

 section, but the shoot-apex is cut somewhat obliquely, as its direction of 

 growth did not coincide with the plane of the section. From a study of 

 this particular plantlet I am still more of the opinion that the embryo 

 gives rise to two main organs only — viz., the foot and the shoot — the 

 former arising from the lower half and the latter from the upper. Whether 

 or not a definite stem-apex is differentiated early in the embryo my 

 material does not show, although the embryo shown in fig. 56 would seem 

 to indicate this. 



Development op the Young Plant. 



A good number of prothalli were found on which single young plants 

 in various stages of development were borne. Also, I dissected out of the 

 tree-fern humus a large number of complete plantlets which had become 



