168 MR. E. C. HORRELL ON THE STERIGMATA 
On the Number of Sterigmata and Spores in Agaricus campestris. 
By E. Cuartes HogkELL. (Communicated by Professor J. 
BnETLAND Farmer, F.L.3.) 
[Read 3rd June, 1897.] 
(Prate 10.) 
NorwrrHsTANDING the fact that the common mushroom, Agaricus 
(Psalliota) campestris, has been described in very many text- 
books, there still exist various contradictory statements as to the 
number of spores borne on each basidium. For this reason 
and also because most of the statements were made some years 
ago, when the methods of preparation were not perhaps so good 
as they are today, it seemed advisable to carefully examine a 
number of specimens of different ages, in order to determine 
the actual amount of variation, if any, and thus if possible to set 
the matter at rest. 
In the first English edition of Sachs's Text-book (1875), in 
the description of, Agaricus campestris (p. 251), the following 
sentence occurs :—'* Each basidium produces in this species only 
two, in other Hymenomycetes usually four spores." Here also 
is the well-known figure, which has been copied into almost all 
the succeeding text-books. In the following year Mr. Worth- 
ington G. Smith, writing on the structure of the Common 
Mushroom (‘ Gardener's Chronicle, 1876, p. 456), says :— The 
spores in all the mushroom tribe are produced in clusters of four 
on each basidium ; but on the common mushroom, and all its 
varieties, as far as I have seen, these four spores are generally 
produced two at a time, and as the first two drop off the last two 
appear, so that it is seldom that more than two are seen in situ 
at the same time.” He adds, “The phenomenon .... has been 
quite erroneously interpreted by Prof. Sachs.” Mr. W. G. 
Smith gives figures showing spores being produced two by two 
on each basidium, but the form of the basidia figured by him does 
not in the slightest degree resemble that of the basidia of 
Agaricus campestris. In 1884 Hesse, in a long paper on the 
structure of the Agarics *, for the purpose of which he examined 
* “ Beiträge zur Classification der einheimischen Agaricineen auf anatomische 
Grundlage," (Verhandl. bot. Vereins Brandenburg, 1884, p. 110.) 
