APPENDIX. 467 



coiled bodies, with a number of fine threads at one end and a 

 little bladder at the other. The threads are for swimming, 

 lashing about and propelling the male cell, which rotates as 

 it advances through the water; the little bladder contains 

 starch a store of food for the journey to be taken by the 

 male cell in its search for an archegonium. In this search, it 

 is helped by an attractive substance given out into the water 

 by the ripe archegonium. The cells in the neck of the arche- 

 gonium become gummy when ripe, and when the gum absorbs 

 water it swells and causes these neck cells to force open the 

 tip of the neck, leaving a clear passage down to the egg-cell. 



PROTHALLUS 



LEAF 



VASC. STRAND 



-- ROOT HAIR 

 i? 

 UNFERTILIZED 



ARCHEG* 

 --- PR. ROOT 



Fig. 7. Embryo of Fern attached to Prothallu*. 

 (Longitudinal section.) 



The gummy liquid that exudes from the open neck of the 

 ripe archegonium contains malic acid, and as this diffuses 

 through the surrounding water it attracts the antherozoids, 

 one or several of which may enter the neck and swim down to 

 the egg-cell. Eventually one male cell enters the egg and 

 blends with it, fertilising the egg-cell, and the fertilised egg 

 then grows into a young fern plant with stem root, and first 

 leaf (cotyledon). We know that malic acid (which is present 

 in apples, and so gets its name) occurs in the fern prothallus ; 

 and if a fine capillary tube is filled with a solution of this 

 acid and pushed under a cover- glass into water which con- 

 tains male cells, the latter swim towards the opening of the 

 tube and crowd into it as if it were an archegonium. 



Returning to our prothallus cultures, after a month or two 

 we notice a few small leaves growing out from the notch, and 

 on turning the prothallus over we can trace these leaves to 



