198 H0FME1STER, ON 



with starch and oil-drops (PL XXVI, fig. 3p.) In the 

 earlier stages these knots are whitish or yellowish in colour ; 

 afterwards their outer side becomes brownish by the forma- 

 tion of from two to three layers of cork- cells. Perhaps 

 these wonderful organs are gemmae, destined to reproduce 

 the proth allium. 



It may be considered as beyond question that the pene- 

 tration of a spermatozoon into the open canal of the neck of 

 the archegonium is necessary in order that the spherical 

 cell within the central cell may be further developed, so as 

 to become a frond-bearing plant. Under ordinary circum- 

 stances the spermatozoa have the means afforded them of 

 swimming to the opening of the archegonium. Whenever a 

 dew occurs, numerous drops of water are found on the 

 under side of the parenchymatal cushion of the prothal- 

 lium. The flat space between the prothallium and the 

 ground is often filled with water. Under such circum- 

 stances, as the ground becomes gradually drier, air-bubbles 

 are formed under the prothallium, and their presence is 

 shown by the silvery-green glimmer which is exhibited by 

 the tissue above them. 



The spermatozoa enter the canal, pass through it, and 

 ultimately reach the interior of the central cell, piercing 

 through the softened membrane of the apex of the latter. 

 Here they move about for some time, sporting actively around 

 the germinal vesicle, which is in close proximity to the 

 inner wall of the central cell near the place of entry of the 

 spermatozoa,* Immediately after the arrival of sperma- 

 tozoa in the embryo-sac the interior of the mouth of the 

 canal is closed by the transverse expansion of its bounding 



* I repeat here, with some additions, the course of observations upon which 

 the above statements are founded, an account of which I have already given in 

 the ' Reports of the Royal Scientific Society of Saxony.' 



"When a quantity of fern-spores are sown, the germinating prothallia are 

 developed at very different periods. The earliest prothallia produce in the first 

 instance only antheridia, afterwards antheridia and archegonia together, and 

 when advanced in age, only archegonia. The earliest prothallia have already 

 attained the latter stage at the time when the later prothallia, the development 

 of which has been retarded by the shade afforded by the earlier ones, are 

 thickly covered with antheridia. If the plants are now kept for some days 

 rather dry, and then saturated with water, the result will be that numbers of 

 antheridia will emit spermatozoa, and numbers of archegonia will open contem- 

 poraneously. The water should not be poured over the plants, but the pot 

 should be placed in water nearly up to its margin, by which means capillary 



