,8^. A NEW GROUP OF FLOWERING PLANTS. 139 



We have thus accounted for the sub-division of the seed-plants as 

 at present accepted. 



Seed-plants (Phanerogams). 



Division I. Division II. 



Gymnosperms. Angiosperms. 



Ovule naked on the carpel. Ovules borne in an ovary. 



Distinct female prothallium present Female prothallium extremely rudi- 



bearing archegonia as in the mentary, and the female organ 



Vascular Cryptogams. reduced to the oosphere. 



Let us now return to Dr. Treub's recent work. He first gives a 

 clear account of the development of the ovary and ovules on which 

 our knowledge has hitherto been " inexact and incomplete." The 

 ovary is formed of two carpels, which at first include an ovary 

 cavity, but the cavity subsequently disappears almost entirely, and 

 is only indicated again when the ovules begin to develop. One is 

 produced from each carpel, but an inequahty is early noticeable 

 between the two protuberances from which they are developed, the 

 smaller forming only a sterile ovule. They are separated by the 

 cellular mass of the placenta and are semi-anatropous. 



Section 2 deals with the sporogenous tissue and the macrospores. 

 The archesporium consists of four large subepidermal cells, by the 

 growth and division of which is produced a fairly thick cylinder of 

 sporogenous tissue in the centre of the nucellus, quite distinguished by 

 the large size of the cells from the enveloping layers. An intercalary 

 growth at the base connects the sporogenous tissue with the chalaza, 

 where the tissue of the nucellus is attached to the funicle or 

 stalk of the ovule. The large cells of the sporogenous tissue are 

 embryo-sac mother-cells. They divide rapidly by transverse walls, 

 which are thick and shiny like the walls of the embryo-sac mother- 

 cells of other Angiosperms. Three differing elements result from this 

 division : 



1. Small cells with a dense protoplasm and big nucleus. These 

 are ultimately, but not at first, crushed and absorbed by the 

 macrospores. 



2. Large cells or macrospores. 



3. Tracheides. These Treub compares with the elaters of 

 Hepatics, though their function is unknown. They occurred in two 

 out of the three species examined. 



The macrospores grow rapidly, producing long tails, which often 

 penetrate the chalaza. The number developing may be considerable, 

 in Casuarina suberosa as many as twenty ; where they are very 

 numerous, some in the region of the micropyle do not produce 

 tails. 



As regards the contents of the macrospores, we must distinguisli 

 between sterile ovules and those which will be fertilised. In the 

 former, Treub rarely saw tails to the macrospores, the latter increasing 



