NUCLEAR PHENOMENA 9 



The spacial arrangements of the basidia and then* successive 

 development certainly require a more detailed study in the Mush- 

 room and fruit-bodies of the same type.^ 



Nuclear Phenomena. — The nuclear changes occurring in the 

 basidia and paraphyses during development have now been investi- 

 gated by modern methods, and it has been found that each hymenial 

 cell, when first formed, contains two nuclei.^ In cells destined to 

 become basidia, the nuclei fuse to form a single nucleus. By means 

 of two successive bipartitions the fusion nucleus then divides into 

 four nuclei, Avhereupon the sterigmata and spores begin their 

 development. When the spores have attained a certain size, the 

 four nuclei severally and simultaneously approach the four sterig- 

 mata, creep through them, and pass into the spores, each of which 

 thus becomes provided with a single nucleus. Whilst making 

 their way into the spores, it is necessary for the nuclei to squeeze 

 through the very narrow sterigmatic necks, which feat is accom- 

 plished by their becoming compressed into slender filaments. 

 The extent to which the nuclei suffer constriction aifords strik- 

 ing evidence of protoplasmic plasticity, and may be regarded as 

 indicating that cytoplasm may move with considerable ease 

 from cell to cell through pits in cell- walls. It seems to be 

 highly probable that a ripening spore becomes cut off from its 

 sterigma by a cell-wall, which eventually becomes double. If 

 this were not the case, one might expect that spore-discharge 

 would be accompanied by the collapse of both spores and basidia ; 

 but this I have observed does not occur.^ However, anatomical 

 evidence of the existence of the double wall just before spore- 

 discharge has not as yet been obtained. 



As the spores are ripening, the basidium is devoid of nuclei. 

 However, its cytoplasm remains living, and is useful in main- 



^ The gills of Panseolus phalxiiarmn and of some allied species become finely 

 mottled at maturity. Numerous ripe spores are to be found on the darker areas, 

 whilst those on the lighter areas are still uncoloured. 



- I have not made any original investigations upon the cytology of the de- 

 veloping hymenium. The facts here given in this connection are taken from 

 the paper by VV. Ruhland, " Zur Kenntniss der intracellularen Karyogamie bei den 

 Basidiomyceten," Bot. Zeit., 1901, Abt. I., pp. 187-204. 



* Vide infra, Chap. XII. 



