XVI PEOCEEDIKGS OF THE 



temal agencies, or again simplified by partial abortions as the same 

 purposes came to be answered by more or less perfect unisexuality 

 or other means. 



If, then, we are right in concluding that Gnetacese cannot have 

 descended from Conifers nor the higher Dicotyledons from Gnetacese, 

 though all may have descended from a common stock, we cannot bat 

 think that Strasburger has failed in proving any genetic homology 

 in their floral envelopes. The question returns, therefore, to its old 

 phase, to be determined by morphology, position, and functions. 



First, as to morphology. In phajuogamous plants, immediately 

 around or amongst the sexual elements the outgrowths from the 

 floral axis are of two kinds, either continuous and uniform or oblique 

 all round the axis, or arising in several separate parts : the former 

 are regarded sometimes as mere axial developments, sometimes as 

 exceptionally single and one-sided foliar organs ; the latter as ap- 

 pendages or leaf-organs, forming part of the general phyllotaxy 

 of the plant. To the fonner class would be refeiTcd diacal ex- 

 crescences and ovular integuments, to the latter carpellary elements. 

 Strasburger shows that the disputed envelope in Conifers most fre- 

 quently, though not always, appears at an early stage in the shape 

 of two more or less distinct opposite protuberances, that it is con- 

 sequently foliar, partaking of the phyllotaxial system of the plant, 

 not axial nor exceptionally monophyllous and unilateral, and that 

 it is therefore carpeUary, not ovular. 



But here we have another element of uncertainty, which has 

 recently been the subject of much controversy, and to which I shall 

 presently revert. The limits between axial dilatations and regu- 

 larly formed appendages are not always definite, and occasionally 

 are wholly obliterated ; and the present case may be included 

 amongst those in which the distinction is ambiguous. Morphologi- 

 cally the seminal envelope of Conifers shows a tendency to enter 

 into the general phyUotaxial system of the plant ; but in several 

 genera it retains the characters of an axial dilatation, or, as Stras- 

 burger interprets it, a single leaf. In Gnetum there is a double 

 inner integument, which he considers enturely ovular or seminal 

 and monophyllous, whilst the outer one is, according to his view, 

 carpellaiy, consisting of two leaf-organs in conformity with the 

 general phyUotaxy ; but he admits (p. 119) that the outer one of 

 the two ovular integuments is traversed by bundles of vessels 

 similar to those of the external carpellary envelope, and " only 

 aff"ords a further proof of the morphological connexion of the two." 



