THE VASCULAR CRYPTOGAMS 71 



archegonia are prepared (consisting of tiny capillary 

 glass-tubes) and filled with a mucilage to which a small 

 quantity of this acid has been added, they are found, 

 when placed in water containing fern-spermatozoids, to 

 exercise the same attraction upon them which the real 

 archegonia exercise in nature. The malic acid gradually 

 diffuses out into the water, and the spermatozoids are 

 influenced by it, so that they move in the direction in 

 which the substance is more concentrated, i.e. towards 

 the tube. Although it cannot be proved that the 

 archegonia themselves contain malic acid, as they are 

 too small for a recognisable quantity to be obtained 

 from them, yet this substance is known to be present 

 in the prothallus as a whole; so there can be little 

 doubt that the natural archegonia owe their attrac- 

 tive influence to the same chemical agent which has 

 proved efficacious in experiment. 



We see, then, that these minute protoplasmic bodies, 

 the spermatozoids, are not only capable of active move- 

 ment, but also possess a certain power of perception, by 

 which their movements are guided. This is a remark- 

 able illustration of the great fact that the protoplasm 

 of plants and animals is essentially the same, and that 

 the living matter of a plant may show properties usually 

 regarded as belonging especially to animals, whenever 

 such properties are needed. 



Now that we have learnt how fertilisation is brought 

 about, we will go on to consider its results 



D. EMBRYOLOGY 



The first change after fertilisation is the formation of 

 a cell- wall around the protoplasm of the fertilised ovum. 



