THE EVIDENCE 73 



The pollen, whether blown by the wind, or, 

 as seems likely to be the case in some South 

 African Cycads, conveyed by insects, is received 

 in the micropyle by a drop of gummy substance, 

 hi which the pollen-grams stick. As the drop 

 evaporates or is re-absorbed, the pollen-grains are 

 drawn down through the narrow passage into the 

 pollen-chamber below (fig. 7, D). Here each grain 

 anchors itself by sending out a branched tube 

 into the surrounding tissue. Thus pollination is 

 effected; the actual fertilisation does not take 

 place for some months later, when the ovule has 

 grown to something like full size and become, to 

 all appearance, a seed. In the interval between 

 pollination and fertilisation, the embryo-sac or 

 megaspore, embedded in the central body of the 

 seed, has grown to enormous dimensions, filled 

 itself with tissue (the endosperm or prothallus) 

 and developed several egg-cells at its upper end. 

 It will be remembered that it is characterstic of 

 Gymnosperms for the endosperm to be formed 

 before fertilisation. In Cycads, everything is on a 

 great scale; even the egg-cells are quite large 

 enough to be seen with the naked eye. Meantime 

 the pollen-tube has also grown much, and, besides 

 other changes, has developed in its ulterior two 

 large cells, the male-cells or sperms. Each of 

 these has a long spiral band round one end, on 

 which a multitude of delicate filaments or cilia 



