EVOLUTION OF PHANEROGAMS 173 



differing, originating as hollow buds or protrusions of ecto- 

 derm and endoderm from the colonial coenosarc. 1 



On page 94 the evolutionary significance of these four 

 forms has already been mentioned, and the fact pointed out 

 that the medusiform gonophore is not a zooid but a 

 megazooid. 



Marine colonies of the present day are, it is true, highly 

 evolved, yet we may believe that in fundamental plan they 

 do not differ from their primitive types ; and our theory 

 suggests that in the marine sporosac and medusiform gono- 

 phore we have the key to Phanserogam evolution ; that 

 from a past type of zooidal colony bearing sporosacs came 

 one of the two divisions of Phanserogams, and from a type 

 bearing medusiform gonophores came the other. In a word, 

 that the marine gonoblastidium (Pig. 28, page 93) which 

 bears sporosacs is homologous with the Gymnosperm cone, 

 and similarly, to an extent which will presently be mentioned, 

 that the attached medusiform gonophore is homologous with 

 the Angiosperm flower. 



If the vegetative " zooids " or internodes of the Gymno- 

 sperm do really represent ancestral vegetative zooids, we 

 expect to find confirmation in the Gymnosperm's reproductive 

 structure, and the next figure shows that we do find it 

 (Fig. 49). 



Naturally, the adaptation of our hypothetical primitive 

 zooidal colony to aerial conditions, and the increased 

 complexity this would involve, would tend to obscure the 

 Gymnosperm's derivation ; but with the clear indications of 

 continuously zooidal derivation offered by the repeating 

 internodes of the vegetative part of the plant it is difficult 

 not to recognise in the pine-cone the terrestrial counterpart 

 of the hydrozoal sporosac-gonoblastidium. In the carpel 

 and stamen we would recognise the central spade of the 

 sporosac. It is not unreasonable to suppose that the dryness 

 of aerial conditions would involve the disappearance of the 

 sporosac-walls, and produce a pre-terminal arrest which left 

 a megaspore and microspore in place of ovum and spermato- 

 zoon ; a certain amount of further cell-division being 

 necessary for the actual production of sexual elements. 

 In the Calamite cone (Pig. 49, G) one also seems to recognise 

 1 See " Megazooidal Individuals," pages 92-98. 



