SPERM-EGG INTERACTING SUBSTANCES, II 47 



fully controlled conditions, particularly as a number of the re- 

 ported cases of attraction are said to be associated with repulsion 

 at the same time. It is of course possible that strong concentrations 

 of a substance may repel and weaker concentrations of the same 

 substance attract, organisms, as in the case of certain flagellate 

 protozoa (Fox, 1921). But interpretation of experiments is more 

 difficult in such cases. 



This chapter is not intended to review all work on the chemo- 

 taxis of spermatozoa towards eggs, but rather to indicate future 

 lines of research which might be profitable. There is, therefore, 

 no discussion of sperm chemotaxis in mosses, for which sucrose, 

 according to Pfeffer (1884), is the only attractive substance. In 

 recent years little work has been done on the chemotaxis of plant 

 spermatozoa, except for a few observations by the author which have 

 been mentioned earlier, one paper by Wilkie (1954), and the work 

 of Cook et al. (1948, 1951). These workers examined the chemotaxis 

 of seaweed spermatozoa [Fucus serratus Linn., Fiicus vesiculosus 

 Linn., and Fucus spiralis Linn.) towards the secretions of eggs of the 

 same species. This work is interesting from two points of view; 

 first, the egg secretions and other substances which attract thal- 

 lophyte spermatozoa are chemically quite diflFerent from those 

 which attract fern and moss spermatozoa ; secondly, in spite of an 

 intensive investigation by organic chemists, which included the 

 examination of sea water containing egg secretions with the mass 

 spectrometer, it was not possible to identify the substance or sub- 

 stances which are produced by seaweed eggs and which attract 

 spermatozoa of the same genus. The mass spectrometer evidence 

 suggested that the naturally occurring substance had a molecular 

 weight of 74; that it contained an Me group which was rather 

 easily lost under the influence of the ion gun; that it had a carbon 

 chain which contained three or less carbon atoms ; and that it did 

 not contain an easily lost hydrogen atom, as in an alcohol group. 

 These considerations raised the possibility that the compound 

 might be diethyl ether; but this compound, though it attracted 

 seaweed spermatozoa, did not do so at the required dilution. 

 Other substances which attract these spermatozoa are «-hexane, 

 i-hexene, sec.-h\ity\ alcohol, and w-propyl acetate. At one moment 

 the normally occurring compound seemed most likely to be n- 

 hexane, but the data obtained with the mass spectrometer made 

 this possibility remote. 



