THE PINE 157 



and at the micropylar end several reduced archegonia 



with very large eggs. 

 Show in an outline drawing the relations of the structures 



described above, treating such details as are possible in 



separate figures. 

 The endosperm, with the archegonia and eggs, constitutes the 

 female gametophyte, derived from a megaspore which became the 

 embryo sac. The megaspore was one of a group of four cells, 

 tetrad, formed in the interior of the nucellus, which is conse- 

 quently a megasporangium. The integument is a special protec- 

 tive envelope, possibly comparable to an indusium. The pollen 

 tubes are later developments of the male gametophytes formed 

 by the germination of the microspores or pollen grains. 



The morphology of the cone scale has been and is still a diffi- 

 cult problem. Because of the arrangement of the fibro-vascular 

 bundles in the scale there are reasons for believing it to be a 

 group of fused megasporophylls or carpels, probably two fertile 

 carpels, each bearing an ovule, and possibly a third sterile carpel 

 represented by the point on the scale, situated above and between 

 the ovules. The cone scale is therefore much more complex than 

 the stamen. According to this theory the cone scale is a group 

 of megasporophylls in the axil of a bract, and the carpellate cone 

 is not a simple cluster of sporophylls arranged along a shoot 

 (like the staminate cone), but is a compound structure consisting 

 of groups of sporophylls in the axils of bracts. The staminate 

 cone has the same morphology as the cones of club mosses and 

 some simple flowers of angiosperms, but the carpellate cone is 

 comparable to an inflorescence, or cluster of flowers, each cone 

 scale representing a highly modified flower. 



K, The gametophytes. A full study of the gametophytes. of the pine 

 would require the examination of stages in material covering many 

 months of development, which is impracticable in a general course. 

 In slides of the stage treated in J it will be possible to determine 

 the following structures : 



1. In the female gametophyte : (a) the delicate cell structure of the 

 endosperm ; (b) the protoplasmic structure of the large egg with its 



