INTRODUCTION TO THE PROBLEM 



the special type of gametophyte to which the name prothallus is given is confined to the 

 Pteridophyta. In none of these cases is meiosis a maturation for the gametes, but it 



Fig. 6. The gametophyte generation of a horsetail {Equisetum). a. Three prothalh of £. sylvaticum L. 

 of various ages mounted in glycerine jelly, x lo. The largest specimen bears a young sporophyte, 

 the uppermost specimen is a young female with a recently fertilized archegonium containing 

 an embryo, and the right-hand specimen is a male with numerous antheridia which appear dark 

 owing to density of contents, b. .\ntheridia of various ages from a whole mount stained in 

 braziline. x 200. Spermatozoids are being extruded from the right-hand antheridium, c. A 

 recently fertilized archegonium with several spermatozoids in contact with the egg cell, the 

 archegonial neck appearing closed and partly shrivelled, perhaps owing to the treatment, from 

 a section stained in haematoxylin, fixed within an hour of insemination, x 200. 



takes an essential part in the formation of the asexual spores and in so doing forms the 

 point of demarcation between sporophyte and gametophyte, the other point of demarca- 

 tion (between gametophyte and sporophyte) being the syngamous nuclear fusion. Some 



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