CH. VIIl] ANTHEROZOIDS. 215 



small ones oi Blechnumfraxineum and Adiantum cuneatum^. 

 They were grown on lumps of peat in the shade of other 

 plants and were used when only about a millimeter in 

 length, and had numerous antheridia but few or no 

 archegonia. They should be kept only moderately damp, 

 as this seems to favour the yield of antherozoids. The 

 prothalli having been washed for a moment are placed 3 

 or 4 together under a small cover-glass supported on 

 strips of paper, and are washed by repeatedly drawing a 

 current of rain water through the preparation. Distilled 

 water, being injurious to the antherozoids, must not be 

 used for the washing, the object of which is to remove any 

 malic acid which may be set free by the rupture or injury 

 of the tissues of the prothallus. The reasons for 

 preferring a small cover-glass are that the antherozoids 

 are thus confined to a smaller space, and that the water is 

 better oxygenated than when a large glass is used. 

 Capillary tubes of O'l to 0'14 mm. internal diameter and 

 from 7 to 12 mm. in length are closed at one end by 

 melting the glass, and are filled with the malic acid 

 solution with the help of an air-pump. The solution may 

 be either the free acid or a salt, for instance, sodium 

 malate ; the solutions should be made with rain water and 

 contain about 0*05 per cent.-. A capillary tube is pushed 

 under the cover-glass, when the antherozoids in the 

 neighbourhood of the opening are at once attracted to it. 

 Pfeffer has seen 60 antherozoids enter a tube of malic 



1 The young prothalli of Ceratopteris, grown from spores sown on 

 bricks, give a good supply of antherozoids. 



2 The strength may vary from 0-01 to 0-5 per cent. 



