Holloway. — The Prothallus and Young Plant of Tmesipteris. 39 



If it were not for the fact that in Lawson's figures of the prothallus 

 some of the pointed ends of the branches are shown as complete and 

 unbroken, I would be inclined to think that his specimens were merely 

 fragments of old prothalli and not complete ones. All the points of 

 difference enumerated above seem to point to this ; and there is another 

 fact which bears upon the same point — viz., that in none of the prothalli 

 figured by him does he show a meristematic region. There is, how- 

 ever, quite another explanation of the differences between our prothalli, 

 which is that whereas mine belong to the form sometimes spoken of 

 as T. lanceolata, which, as I have shown, differs from the other form, 

 T. tannensis, not only in general habit but also in certain histological 

 details, Lawson speaks of his prothalli as those of T. tannensis. We have 

 become so familiar with the fact of the manifold variations in the types of 

 prothallus of the different species in the genus Lycopodium — new variations 

 being found in almost each additional species discovered — that it is not 

 unlikely that the prothalli of Tmesipteris as described in the two accounts 

 will be found to be those of two different forms which have hitherto been 

 grouped under the collective name T. tannensis. The fact that Lawson's 

 prothalli were obtained by him almost singly from widely different localities 

 and in different years indicates that they represent a constant type of 

 prothallus. 



The prothallus of Tmesipteris shows certain resemblances, such as its 

 cylindrical, radially symmetrical, and more or less drawn-out form, its apical 

 growth, and its branching, to certain other pteridophytic types of pro- 

 thallus, such as those of the epiphytic Lycopodiaceae and Ophioglossaceae 

 and Helminthostaehys. But these resemblances are only what might be 

 looked for in prothalli having the same epiphytic habit. Even with regard 

 to these general characters the resemblance does not hold quite closely, 

 whereas in the. matter of other main features, such as the nature of the 

 basal (or k primary tubercle ") region, the distribution of the fungal 

 element, and the differentiation of vegetative and reproductive regions 

 in the prothallus, there are striking differences. Thus on a general sum 

 of characters the prothallus of Tmesipteris stands apart from that of both 

 the Ophioglossaceae and the Lycopodiaceae. Still less does it show any 

 evidence of affinity to the prothallus of Equisetum. This conclusion is 

 strengthened by a comparative study of the sexual organs, embryo, and 

 young sporophyte. The antheridium is strongly projecting in a manner 

 almost resembling that of the male organ of the leptosporangiate ferns, 

 whereas that of the Ophioglossaceae and Lycopodiaceae is sunken. How- 

 ever, in the manner of its development it agrees with that of the two latter 

 orders. The archegonium also is peculiar in that there is apparently no 

 basal cell cut off in the young rudiment, and the form of the mature 

 organ is very characteristic. It is not certain from which primary half of 

 the young embryo the shoot and the foot respectively develop, or whether 

 there is or is not a suspensor present. But the peculiar development of the 

 foot into long haustoria-like processes, the total absence of a root, and the 

 dominance of the shoot mark out the embryo of Tmesipteris as bearing 

 very little resemblance to that of any other class of Pterid.opb.ytes. From 

 the single embryo found by him in which three lobes were present on the 

 lower half Lawson is inclined to interpret one of these lobes to be the 

 rudiment of the root, ascribing the others to the foot. The fact that in 

 older stages there are a large number of these lobes present, and that they 

 are all similar in appearance, seems to me to indicate that they are nothing 

 more than haustorial outgrowths; and this would also appear to be borne 



