700 EEPORT — 1891. 



6. On the Nuclei of the Hymenomycetes. By Hakold "Wagee. 



In this paper an account is given of some observations upon the structure and 

 changes v^hicli take place in the nuclei of the basidia of Agaricus {Stropharia) 

 stercorarius. Rosenvinge states that the young basidia of the various species of 

 Hymenomycetes which he has examined never contain more than one nucleus. 



In A. stercorarius and other species of Agarici which I have examined, I have 

 found in the very young basidia txco nuclei ; these probably pass into the basidia 

 from the hyphre. At this early stage each basidium contains a small quantity of 

 protoplasm and one" or more vacuoles. 



The two nuclei fuse together to form a single large nucleus which is placed near 

 the centre of the basidium. The basidium then becomes filled with a dense 

 protoplasm containing no vacuoles. 



The structure of the nucleus is similar to that of the higher plants ; it consists 

 of a nuclear membrane enclosing a dense nucleolus and a thread-like network. 

 The nucleolus stains very deeply, the threads slightly. 



As the basidium increases in size so also does the nucleus. The latter places 

 itself near the apex. of the basidium. The nuclei vary in size, generally speaking 

 they are from 3'5 to 4 fi.in diameter, but some of them have a diameter of 4'5 to 

 5 p.. The nucleoli are about 1 '9 to 2 ^ in diameter. 



The nucleus now divides, first of all into two and then into four. The division, 

 which is an indirect one, takes place before the appearance of the sterigmata. 

 Previous to the division, the nucleus elongates slightly towards the apex ; its 

 outline becomes somewhat irregular ; the thread-like network accumulates at the 

 apex, and the nucleolus takes up its position at the opposite end of the nucleus. 

 The nucleolus gradually disappears, and at the same time a group of deeply stained 

 short threads or granules appears in place of the thread-like network at the upper 

 end of the nucleus. 



At this stage the nuclear membrane seems to have disappeared, but a some- 

 what irregular and somewhat clear s])ace surrounds both the nucleolus and the 

 deeply stained chromatic elements. These latter separate into two groups which 

 pass to either side of the basidium. In this way two new nuclei are formed 

 which are small at first, but gradually increase in .size, and have a structure similar 

 to that of the parent nucleus. The two new nucleoli appear to be formed from 

 the chromatic elements. The two nuclei then elongate and divide in the same 

 manner as the primary nucleus. The four nuclei thus formed have a structure 

 ■similar to the parent nucleus, but are much smaller. 



Previous to the development of the sterigmata, they pass to the lower end of 

 the basidium, where they come into such close contact with each other as to 

 appear as if fused together ; it is not quite certain whether fusion does or does not 

 take place ; in any case they undergo certain changes resulting in the accumulation 

 of a more or less irregular mass of chromatin on their walls. This chromatin 

 presents the appearance of a very loose network surrounding the four nucleoli. 



While these changes are taking place, the four sterigmata appear at the apex 

 of the basidium. At the apex of each sterigm a a spore is produced ; protoplasm 

 from the basidium passes into the spores. 



The nuclei at the base of the basidium now separate and pass to the apex ; 

 •each nucleus takes up a position at the base of one of the sterigmata, and this 

 position they retain for some time. The protoplasm of the basidium becomes 

 more and more vacuolated as it decreases in amount. Finally, nearly the whole 

 of it passes into the spores. 



The outline of each nucleus gradually disappears ; the nucleolus becomes 

 smaller — small enough to pass without difficulty into the spore, but whether such 

 a passage takes place or not I have not been able to determine. The spores 

 certainly do not contain a nucleus until a very late stage, e.g. after the formation 

 of the thick spore membrane. 



When the spores are ripe they are seen to contain two nuclei, probably derived 

 from the single nucleus which passes into them in some way or other from the 

 basidium. 



