214 Transactions. 



The question arises as to whether the ancestral type of prothallus was 

 compact and massive or long-drawn-out and delicate in nature. Being 

 situated at the surface of the ground, it would seem that the prothallus 

 would be short rather than filamentous. This would be in accord with 

 the fundamental structure-plan of the prothallus as seen in all the modern 

 Lycopodiaceous types, in which the lower first-formed vegetative region 

 has the form of an inverted cone, and apj)ears especially likely from the 

 fact that this form occurs not only in the Inundata-Cernua group but in 

 L. Selago also when the prothallus is surface-growing. However, on the 

 other hand, we are probably not to assume that the '" primary tubercle " 

 is a primitive feature, for it seems to be abundantly clear in the three 

 species L. cernuum, L. laterale, and especially L. ramulosum that these 

 tubercular swellings are due simply to the localized presence of a fungus 

 element which was, of course, not an original feature of the prothallus. 

 In the prothalli of the Selago, Phlegmaria, clavatum, and complanatum 

 types the increase in girth from the spore upwards is always rapid, there 

 being apparently no filamentous stage at all ; but this can be readily 

 explained by the fact that infection by the fungus seems there to take 

 place from the very beginning. Also in L. cernuum this is apparently the 

 rule, so that the tubercle constitutes the basal portion of the prothallus ; 

 but in L. laterale and L. ramulosum there is generally a well-marked fila- 

 mentous stage. The young prothalli of both these species are green from the 

 first and remain free from fungus for a considerable period, assuming during 

 this stage the form of an elongated flat filament of cells which shows no 

 localized tubercular swelling of its tissues. Even some of the largest and 

 most drawn-out forms of prothalli of L. ramulosum are seen to have their 

 basal region of this form (16, figs. 32b and 32d), the increase in girth of the 

 prothallus having taken place very gradually and the infection of it by the 

 fungus being not localized in one much-swollen region but distributed over 

 several distinct areas. Thus it is probable that the primitive, wholly self- 

 nourishing type of prothallus was filamentous rather than massive, and 

 that the erect growth and radial build came later as the result of the more 

 rapid development of the tissues consequent on the infection of the lower 

 region by the fungus element. 



The " mixed " type of stelar anatomy with much-extended protoxylem 

 groups characteristic of the Inundata and Cernua sections is in striking 

 contrast with the definitely radial type which is the primary stelar 

 structure of the rest of the genus. This mixed type is initiated by the 

 precedence of the leaf -trace system over the cauline cylinder in the young 

 plant, but is marked throughout the whole life of the plant. This 

 character, along with others that have been mentioned, gives to the 

 Immdata-Cernua group a position definitely apart from the other sections 

 of the genus. 



Thus, although some of the main characters of the species of these two 

 sections are probably recent and adaptive, especially as regards the external 

 form and habit of growth of the sporophyte, others are undoubtedly 

 primitive. Also, the possession of a protocorm stage in the embryogeny, 

 and the mixed type of stelar anatomy, brand these sections as together 

 standing very much apart from the other sections, which, as we have seen, 

 are probably somewhat closely interrelated. Being thus primitive in some 

 respects and modified in others, the Inundata and Cernua sections are best 

 considered to be a natural division of the genus whose ancestors diverged 

 from the ancestors of the Selago stock at a probably early period. 



