K.— BOTANY. 189 



primary mycelium, and their germinatiuu among hyphse of opposite strain 

 may initiate the secondary condition. 



Even in that incalculable group, the fungi, there are few things more 

 curious than the formation of clamp-connections and the method of 

 nuclear division which has been described as associated with them. 

 The cells of the secondary mycelium are binucleate, one nucleus being 

 presumably derived from each of the primary mycelia. Simultaneous 

 division of two or more nuclei present in the same cell is almost universal 

 in plants, and such a division, with spindles parallel to the long axis 

 of the filament — the natural position in the narrow cells of a hypha — 

 would readily separate two freshly formed nuclei from their sisters. 

 Instead of this, the cell grows out laterally, forming a branch which 

 at once bends round and fuses with the cell of origin. One of the 

 daughter nuclei, still attached to its spindle, wanders through this 

 branch, or clamp-connection, and so rejoins the daughter nucleus of 

 the other member of the pair. Both in the main cell and in the clamp, 

 walls appear and the division is complete. It would be of interest 

 to know either the origin, or the use — if any — of this elaborate procedure ; 

 it is not a subject on which I feel able to hazard a guess. Whatever their 

 relation to the nuclei, clamp-connections, when present, form a convenient 

 means of recognising the secondary mycelium and the associated binucleate 

 condition. It may be noted that their occurrence is not universal, 

 Coprmus epJiemerus and G. curtis, for example, developing without them in 

 mass culture^^. 



In many of the Hymenomycetes the binucleate condition does not 

 arise till the formation of the sporophore is well advanced. In mushrooms 

 the cap and stem are composed of multinucleate cells, binucleate cells 

 appearing first in the gills^^. In Boletus granulatus the cells of the stalk 

 are multinucleate, whereas those of the ring and of all parts of the cap 

 contain two nuclei-". In other forms, as in Coprinus, the sporophore is 

 made up wholly of binucleate cells. There is evidence that in nature, in 

 such cases, the sporophore is derived from two spores in heterothallic 

 species, and, in homothallic species, from a single spore-^. Where part 

 of the sporophore consists of multinucleate cells, the species is presumably 

 homothallic, though the possibility is not excluded that several similar 

 mycelia may share in the construction of one fructification, or that fusions 

 may occur between them. 



Since Kniep's and Bensaude's discovery a very full study has been 

 made of heterothallic members of the Basidiomycetes. In some cases the 

 primary mycelium, if it does not encounter an appropriate strain, appears 

 to remain permanently sterile ; in others it sooner or later produces 

 clamp-connections and sporophores. This was observed, for example, in 

 Coprinus Rostrupianus,^^ where fifty-six per cent, of the single-spore 

 mycelia became spontaneously diploid in the course of six months. 

 Similarly Vandendries found that in the wild-fruit bodies of Paneolus 

 campanulatus and P. separatus,^^ some of the spores were definitely (+) 

 or (— ), but a considerable number gave positive reactions with strains of 

 both kinds. Nor is the number of strains limited to two ; in Aleurodiscus 

 polygonus^^'^ Coprinus lagopus^^ and other species, four strains are found, 

 only the appropriate pairing being fertile. The character of the strains 



