218 PHILOSOPHICAL NOTES ON 



Similarly, the anther of the Iris is dorsal or extrorse, that is, 

 it dehisces on the back like the indusium of most ferns. In 

 reality it consists of no other than a pair of sori on the contracted 

 back of a staminal frond, jfilled with pollen grains — the homologues 

 of spores. 



The stamens of Zamia Muricata (Sachs, Fig. 344) resemble 

 nothing more closely than the peltate indusia of Aspidium 

 Lonchifis, Sw., and others, in which the peltate indusium had 

 become thickened and adherent to an expansion of the placenta 

 which bears the sporangia.* The pollen sacs of this Zcwiia 

 bears a close resemblance to the sporangia of Ophioglossium and 

 Botrychium. That they are differently grouped would signify 

 little, for we see sporangia, which nobody denies are sporangia, 

 differently grouped in different ferns. 



We have only to examine almost any male cone of conifers, 

 including Salisburia, and of Cycads to find homology with the 

 sori of ferns. They are situated dorsally, and of course modified 

 in various ways. 



In Porphyra laciniata, as Thuret has shown, we have the 

 cells of the leaf becoming the mother cells of pollen. The cradle 

 of pollen is not here specialized as in the anther, but is still 

 generalized. Pollen, or its other name antherozoids, is produced 

 in any vegetative cell of the leaf. This shows us that there is no 

 essential difference between vegetative and rejDroductive cells. 

 The separation exists in the higher plants as a useful sub-division 

 of labour. 



Moreover, Thuret states that there is no fundamental difference 

 in the process of evolution between male and female elements of 

 this alga, for in abnormal cases the contents of the primitive cell 

 change partly into female and partly into male elements. All the 

 cells of the frond do not become fertile, for here and there are 

 found vegetative cells which have not undergone transformation. 

 In other words, we might say that what we call vegetative cells are 

 abortive reproductive cells. 



The indusia of ferns and their sporangia are a further 

 specialization of the reproductive cells. In Porphyra laciniata 



* I call it placenta because I do not see that it is anything else. It is 

 borne on a vein or axis. 



