212 Transactions. 



be the normal rule in L. Selago — at any rate, in its surface -growing forms — 

 and the latter in the prothallus of the Phlegmaria section. It is signifi- 

 cant to note that both these methods of growth are represented in those 

 New Zealand species which belong to the Cernua section, and which are 

 described later in this paper, although in these species they are not so 

 clearly differentiated as in the former. The prothalli of the Phlegmaria 

 section represent the extreme attained within the genus by the elongated, 

 cylindrical type of growth, and the prothalli of the clavatum and com- 

 planatum sections represent, on the other hand, the extreme attained by 

 the continued cone-like manner of growth. The prothalli of L. Selago, as 

 Lang has pointed ojit (10, p. 305), show that these two main types are 

 not fundamentally dissimilar, for they both here occur in the same species. 

 In saying this, however, it must clearly be remembered that, according 

 to Bruchmann's account, the elongated, cylindrical forms of the L. Selago 

 prothallus do not altogether correspond to the ' elongated prothalli of the 

 Phlegmaria section, for growth in them is not truly apical, but is rather 

 a one-sided marginal extension from the cone. The elongated prothallus 

 of L. ramvlosum, as will be shown, is really more comparable to the 

 prothallus of L. Phlegmaria, &c., although, even here, the comparison is 

 not an exact one. The elongated bilateral extensions from the basal cone 

 in L. Selago are better compared with the flattened extension from the 

 margin which Bruchmann described and figured in L. annotinum (1), being 

 of the same nature but much more pronounced. 



The more compact surface-growing form of the L. Selago prothallus is 

 nearer to a self-nourishing, chlorophyllous type of prothallus, which must ' 

 certainly be regarded as more primitive than a wholly saprophytic one. 

 The very young prothallus, as has been said, begins with the cone form, 

 and next has to set apart a central conducting-core which reaches up 

 behind the actual growing apex. The apex, of course, will be more or less 

 conical in shape, and at this stage is certainly not brosid. If the pro- 

 thallus does not proceed to elongate rapidly, the stimulation to increase 

 in size will be largely confined to increasing its girth, and this will take 

 place not only by a broadening of the apical mersitem, but also by divi- 

 sions taking place in the body-cells generally. At the same time the 

 fungus-free central core will extend in width as the apex broadens and 

 the prothallus slowly extends in length, until it assumes above the form of 

 a cushion of tissue. If chloropyhll is developed in it, this upper cushion 

 will contain a general distribution of starch. In proceeding to explain 

 how the original apical meristem could become transposed to a marginal 

 ring it seems not unnatural to suppose that as the upper fungus-free 

 tissue becomes more bulky, and so loses the tendency to a localized 

 concentration of food material, the stimulation exerted by the supply of 

 food is felt more in those parts of the prothallus where the fungus is 

 youngest and therefore in its fullest functioning power. This will naturally 

 be along the upper margin of the enveloping fungal zone which extends 

 as a ring around the prothallus. Here, then, the meristematic activity 

 of the prothallus will be localized. As the prothallus still continues slowly 

 to increase in size the fungus will push forward bit by bit into the more 

 newly formed cells, the prothallus still retaining the original cone form. 

 I . In the surface-growing prothallus of L. Selago this is what happens, 

 and the sexual stage is fairly early initiated, the antheridia and later the 

 archegonia arising from the meristem. A comparative study of the pro- 

 thalli of the different species of Lycopodium shows that the cone type of 



