X THE HOMOSPOROUS LEPTOSPORANGIATAi 355 



are present. The chromosomes are not conspicuous, a con- 

 dition that we have seen before is not uncommon in the ees: 

 nucleus. 



A curious appearance was noted several times just before 

 the archegonium seemed about to open, and after the formation 

 of the ventral canal cell. This was the separation from the 

 upper part of the ^gg of a small lx)dy containing what looked 

 like a nucleus. Whether this is something analogous to the 

 "polar body" found in animal ova could not be determined. 



When the archegonium opens, the four rows of cells bend 

 strongly outward, and frequently some of the terminal cells 

 become detached. A large receptive spot is present, and the 

 nucleus is smaller than in the younger ^gg, and contains more 

 chromatin, and usually but a single nucleolus. 



Fertilisation 



The horizontal position of the archegonia, as they project 

 from the sides of the midrib, makes it easier to follow the en- 

 trance of the spermatozoid than is the case in most Ferns. The 

 spermatozoids collect about the mouth of the freshly-opened 

 archegonium, and soon one finds its way in. With the ciliated 

 end down, it revolves rapidly, not seeming to be much impeded 

 by the mucilage thrown out by the archegonium. Suddenly, 

 with a quick movement, quite unlike the slow worm-like move- 

 ment seen in most Ferns, it slips through the neck into the cen- 

 tral cavity, where its movement is resumed. After about three 

 or four minutes it disappears, and has presumably penetrated 

 the Qgg. Other spermatozoids may make their way into the 

 central cavity, but only one penetrates the ovum. The lower 

 neck cells now approach, but not enough to prevent the entrance 

 of other spermatozoids. Within a few hours the inner walls 

 of the neck cells begin to show the brown colour that indicates 

 that fertilisation has been accomplished. 



The Qgg quickly secretes a cellulose membrane, which pre- 

 vents the entrance of the other spermatozoids. The egg nu- 

 cleus moves towards the receptive spot at the time of fertilisa- 

 tion, where the spermatozoid may be seen but little altered in 

 form. It almost at once comes into contact with the female 

 nucleus, and the two then move toward the centre of the ovum. 

 Here the spermatozoid gradually loses its coiled form and con- 



