Page:Proceedings of the Royal Society of London Vol 69.djvu/305

Rh and recent writers, as Vines, Bower, Campbell, Goebel, Pritzel,* distinctly state that the development of Phylloglossum is not known. I have not had access to Crie"s original account, and Bertrand,t who quotes Crib's statements, was unable to obtain a germination of the spores during six years' experiments. But in any case it is clear that Crie"s account was incomplete, for the prothallium becomes green, and even vividly green. According to Bertram!, Crie can only have seen the tubercle which precedes the prothallium proper.

It is not improbable that the prothallium may start life as a sapro- phyte, aided by the endophytic fungus, and I have found a young prothallium which was quite colourless save for a faint yellow tinge at the upper end, as well as two others, still without sexual organs, which showed only scanty chloroplasts. It is quite probable that on the germination of the spore the tubercle is first formed, and when this is at too great a depth in the soil to receive any light, it will doubtless be colourless. But I have never observed any fully de veloped prothallium that was not green above, whilst all prothallia which had succeeded in producing an embryo had reached the surface and attained a considerable development of chlorophyll.

A comparison of the prothallium of Phylloglossum with those of the few species of Lycopodium in which the gametophyte is known, shows that it is distinctly of a Lycopod type. But, as is well known, there is a remarkable diversity amongst the prothallia of the different species of Lycopodium. On the whole the prothallium of Phyllo- glossum probably resembles a prothallium of the L. cernuum type more closely than any other, though it is quite without the leaf-like assimi- latory lobes of L. cernuum. Perhaps we are justified in regarding it as the simplest known type amongst the Isosporous Lycopodinae.

The general simplicity of the structure of the prothallium of Phyllo- glossum seems to favour the view that it is a primitive form of Lycopod. It is of course recognised that Phylloglossum is a perma- nently embryonic form, but the simplicity of structure of the mature sporophyte does not necessarily prove that it is a primitive form of the Lycopodiaceous phylum. Bower has expressed the view that Phylloglossum is probably a reduced form, and the absence of transi- tions between the simple cylindrical pointed protophylls and the scale- like sporophylls so like those of some species of Lycopodium may favour this view, if we regard these structures as homologous. Some observations which appear to be new may throw some light upon this question. Bower states that Phylloglossum has been seen branched. I am able to say that branching occurs in at least two distinct ways :

in Engler and Prantl 'Die Naturlichen Pflanzen-familieu,' Lief. 205 (1900), p. 575.
 * E.g., Goebel, 'Organographie der Pflanzen, 2te Toil, 1900," p. 439. Pritzel

t ' Archives Botaniques du Nord de la France/ 1886, p. 221.