68 RESEARCHES ON FUNGI 



Hein's supposed lateral fusions we may call side-to-side fusions 

 and in this way clearly distinguish them from the other types of 

 fusion already described in this Chapter. 



It seems to me that Hein has misinterpreted his preparations 

 and that we are not justified in accepting the view that side-to-side 

 fusions take place in Psalliota campestris either in the ordinary 

 vegetative mycelium or in the mycelial cords. The supposed side- 

 to-side fusions which Hein shows in his Figs. 12 and 13 are evidently 

 very short local peg-to-peg fusions of the kind illustrated in this 

 Chapter in Fig. 16 (p. 32) ; and the evidence which Hein brings 

 forward to support his contention that the large vascular elements 

 in the strands of Psalliota campestris develop not as in Merulius 

 lacrymans by the swelling of individual hyphae, but by the side-to- 

 side longitudinal fusion of a number of smaller hyphae which are in 

 contact with one another, seems to me to be entirely unconvincing. 



Action at a Distance in Vegetative Hyphal Fusions and its Theo- 

 retical Explanation. — As a result of precise experiments made by 

 Pfeffer and others we have become acquainted with the phenomena 

 of chemotaxis and chemotropism ; so that we attribute: (1) to 

 chemotactic stimuli the movements of the spermatozoids of Ferns, 

 Mosses, and their allies toward the mouths of archegonia, the move- 

 ments of bacteria toward or away from oxygen, hydrogen bisulphide, 

 meat extract, and other chemical substances, and the movements of 

 white blood corpuscles toward the surfaces of wounds ; and (2) to 

 chemotropic stimuli the growth-movements of pollen-tubes toward 

 stigmas and the mouths of ovules. On the basis of our knowledge 

 of chemotactic and chemotropic phenomena in other organisms, we 

 are justified in attempting to explain the telemorphic and zygotropic 

 reactions which take place in connexion with sexual and non-sexual 

 hyphal fusions in Fungi as being due to chemical excretions. 



Already, as set forth in the introduction to this Chapter, Burgeff 

 has sought to explain the mutual telemorphic and zygotropic reac- 

 tions which take place in heterothallic Mucorineae when ( +) and 

 ( _ ) mycelia come near to one another as being due to the excretion 

 of two sexual substances, one excreted by ( +) mycelia and ( +) zygo- 

 phores and the other by (— ) mycelia and (— ) zygophores. 



In the mycelia of the Ascomycetes, Basidiomycetes, and Fungi 



