TYPICAL FORMS OF PLANT KINGDOM 101 



a small number of large spores, and the microsporangia, which 

 produce a large number of small spores. The large spores only 

 give rise to female prothalli bearing archegonia, and the small 

 spores only to male prothalli bearing antheridia. 



3. In the spore-producing tissue of the macrosporangia the 

 spores cease to be individualized and invested with their pro- 

 tective membrane. This tissue remains neutral ; the archegonia 

 are directly formed there, and each one is itself reduced to 

 an oosphere surmounted by four or eight cells representing 

 the neck. In the microsporangia, on the contrary, the spores 

 become individualized, but the prothallus which they contain 

 consists simply of three cells of which one, the generative, 

 can give rise by subdivision to eight or ten small cells 

 (Microcycas colocoma of Cuba), each producing two 

 antherozoids, or the generative cell can itself directly produce 

 two antherozoids only (Cycas, Ginkgo). 



4. Lastly the antherozoids cease forming their helicoid 

 band of waving cilia and are reduced to a simple nucleus. 



These modifications can already be produced without 

 changing the form of the vegetative system, as Grand 'Eury 

 has observed in certain fossil Ferns. They are characteristic 

 of the reproductive system of gymnospermous Phanerogams, 

 but the names of the various parts we have just enumerated 

 must in this case be changed, because the reproductive system 

 of Gymnosperms was at first compared with that of Angio- 

 sperms, for which botanists have created a special terminology. 

 Thus, the macrosporangium becomes the ovule ', the tissue 

 corresponding to the prothallus, the endosperm, and the 

 archegonia are the small bodies, each corresponding to an 

 embryo sac. The microsporangia, in their turn, become the 

 pollen sacs, and the microspores the pollen grains. At the same 

 time the modified leaf that bears the macrosporangia becomes 

 the carpel, and that which bears the microsporangia, the 

 stamen. 



The transformation of gymnospermous Phanerogams into 

 Angiosperms is accomplished very simply by a renewed 

 progress of tachygenesis. The carpels, instead of remaining 

 spread open, and leaving the ovules unprotected, as in the 

 Gymnosperms, 1 which derive their name from this fact, are 



1 From yvfivos naked and ontpfia grain. 



