504 Fischer . — On the Development of the Fructification of 
channel, in the form of a narrow ring open towards the outside, arises in the 
upper part of the body by means of separation of the tissues. The portion 
above becomes the pileus and that below the stipe. By later growth, down- 
wards from the pileus and upwards from the stipe, two interweaving series of 
hyphae are formed, thus giving rise to the veil, which covers the air-space. 
Atkinson observed a very different course of development in Agaricus 
campestris. He supposes that De Bary may not have studied the very 
young stages, and states that it would seem that ‘ he adopted Hartig’s sug- 
gestion that Agaricus campestris followed the same course as that described 
by Hartig for Agaricus melleus ’, and in this way the statements current in 
textbooks (4) may have originated. 
Having obtained a number of young fructifications of Ar miliaria 
mucida in pure cultures, I undertook a study of the development of the veil 
in that species, and, as will be seen, my observations agree essentially with 
those of Atkinson. 
Atkinson seems to accept Hartig’s account of the development in 
Ar miliaria mellea as substantially correct, but believes that De Bary was 
mistaken in admitting a similar process for the case of Agaricus campestris. 
As a result of my own investigation I am led to the conclusion that either 
Hartig’s observations must be faulty, for the reason put forward by 
Atkinson, or else the development in two such closely allied species as 
Ar miliaria mellea and A. mucida is entirely divergent. I venture to suggest 
that such a divergence is not probable, and that the course of development 
is similar to that described by Atkinson for Agaricus campestris and as 
set forth below for Armillaria mucida. It must also be remembered that 
at the date of Hartig’s work the improved methods we can now command 
were unknown. 
The fungus was grown on bread and on sterilized beech wood, and 
sporocarps in all stages were taken for the investigation. Three naturally- 
grown very young carpophores were also obtained for comparison ; no 
differences were found between those from the two sources. 
At first I failed to realize at what a very early period differentiation of 
the tissues took place, and had to take specimens of a much younger age. 
Before there is any external indication of a distinct separation of the pileus, 
there is an internal differentiation of the tissues, as described later. 
The sporocarps were fixed in chromo-acetic acid and microtomed. 
The sections were stained with various stains. Eosin gave very good 
results, though, unfortunately, the stain is not lasting. Gentian violet 
followed by orange G or Bismarck brown was also used, as well as Heiden- 
hain’s alum-haematoxylin followed by orange G. The latter method gave 
the most satisfactory results. All the drawings were done with the aid of 
the camera lucida . 
The youngest stages examined, about half a millimetre in length. 
