1040 EEPORT— 1898. 



antithetic view tlie two generations are not homogenetic ; but they may be in a 

 high def^ree homoplastic, and this homoplasy may be impressed upon the two 

 generations, even in the same species, as in some Lycopods. I have never felt the 

 ■cogency of the fact that the gametophyte of L. cermmm is somewhat similar in 

 outline to the young sporophyte. Both generations are exposed to similar circum- 

 stances, and may be reasonably expected to have reacted alike. Moreover, the 

 similarity of form of the ' leaves ' of prothfiUus and plant is but slight, and is not 

 maintained in allied species. Their arrangement is variable. Between them also lies 

 the essential structural difl'erence, so widespread among Archegoniate plants, that in 

 the sporophyte stomata and intercellular spaces are present, in the gametophyte 

 they are absent. These are just such differences as point to homoplastic develop- 

 ment. 3[ore commonly, however, the homoplastic development is only seen in 

 ■distinct organisms, and in this sense we shall rank the leaf of the Moss as the 

 homoplast, but not the homogene, of the leaf of a Lycopod or of a Fern. 



Theory of the Strobilus. 



vSome years ago I submitted to the Section a theory of the strobilus in 

 Archegoniate plants. Comparisons were drawn between Pteridophytes and 

 Bryophytes, and it was suggested that the origin of the strobilus of the former 

 was 'from a body of the nature of a sporogonial head.' I specially pointed 

 ■out at the time that my object was not a mere hunt after homologies, but to 

 obtain some reasonable view of the methods of advance in Archegoniate plants. 

 I wish to lay special stress upon this, for some appear to think that by denying an 

 homology which I have not been at pains to maintain, they invalidate this search 

 after the methods of advance. The Bryophytes as we now see them are our best 

 guides in the search after these methods, even though they may not have been in 

 the direct line of descent of Vascular Plants. As regards the comparison of the 

 strobilus with a sporogonial head, I wish to make it clear that a Moss sporogonium 

 is not specially indicated. The expression used has been ' the origin of the 

 strobilus from a body of the nature of a sporogonial head ' — that is simply a part 

 of the sporophyte which bears spores internally as distinct from a lower vegetative 

 region. We see in more than one sequence of Bryophytes how in a sporogonial 

 bead, as thus defined, the spore-production becomes restricted in extent, and 

 relegated towards a superficial position by the formation of a central sterile mass. 

 I am ready to join Dr. Scott in his confession of inability to find anything like 

 an intermediate form between the spore-bearing plant of the Pteridophyta and 

 the spore-bearing fruit of the Bryophyta, and to agree that at the best there is 

 nothing more than a remote parallelism not suggestive of affinity ; but none the 

 less I think we should continue to search among the Bryophyta for suggestions as 

 to the methods of advance, and to have confidence in transferring these ideas across 

 the gulf, for I believe this to be both a reasonable and a promising method of study. 



DORSIVENTRALTTY. 



Interesting questions arise in connection with dorsiventral structure. In 

 the Equisetinete, and almost all Lycopodinese, the strobilus is of the radiate type, 

 therein corresponding to the radial structure of typical sporogonia. While 

 certain Ferns are of the radiate type, others are conspicuously dorsiventral, even 

 from their earliest embryonic state. Dorsiventral structure also appears in the 

 vegetative region, and sometimes, though rarely, in the strobilus of SeJaginella. 

 Professor Goebel, in a chapter of his ' Organographie,'the publication of which may 

 be recognised as the leading event in the morphological studies of the year, discusses 

 the origin of the dorsiventral state iri a number of examples, and his results have 

 a most interesting bearing on our theory of the strobilus. 



He shows in the case of Vaccinium Mgrtillus how the first shoot of the seedling 

 is orthotropic and radial ; the lateral shoots, formed after the apical growth of this 

 is arrested, are also orthotropic, but the lateral shoots of higher order become 

 plagiotropic with leaves in two lateral rows. He points out the intermediate stepa 



