THE DEVELOPMENT OF AGARICUS ARVENSIS 
AND A. COMTULUSi 
Geo. F. Atkinson 
The development of Agaricus campestris^ from the very young 
and undifferentiated carpophore was published in 1906. In 1905 
young carpophores of several species of agarics in different stages of 
development were collected in the forests of the Jura Mountains in 
the vicinity of Pontarlier, France, during a three weeks' sojourn at that 
place. Among these were Agaricus arvensis Fr., and Ag. comtulus Fr. 
MATERIAL AND VERIFICATION OF SPECIES 
The material for the study of Agaricus arvensis was collected in a 
dense spruce forest, to the north of Pontarlier, maintained by the city 
government. The young carpophores were found in the forest mold 
in connection with the mycelium of a large plant which was not quite 
mature, i. e., not fully expanded. The large immature individual was 
taken to my provisional laboratory in the hotel, photographed before 
the rupture of the veil, and then kept for a day or two for photograph- 
ing in the fully expanded state. There may be some question as to 
whether this plant is Agaricus arvensis or Agaricus xanthodermus 
Genev. (= Ag. ftavescens Roze, not ^g. flavescens Gillet) . Other plants 
collected in the same forest, and communicated to M. Emile Boudier, 
of Montmorency, near Paris, were determined SiS Ag. xanthodermus. 
The single plant from the same mycelium as the young carpophores 
could not well be sent to M. Boudier since it was immature when 
collected and it was desirable to keep it until expanded for the purpose 
of photographing it. 
The important characters of the plant noted at the time are as 
follows: Pileus and stem pure white, pileus smooth or with very fine 
appressed scales. Veil thick, ample, slightly cracked radially at the 
margin and with regular, angular scales on the under side of the margin. 
The flesh remained unchanged where bruised, and the surface of the 
1 Investigation prosecuted with the aid of a grant from the Botanical Society 
of America in 1905. 
2 Atkinson, Geo. F. The development of Agaricus campestris. Bot. Gaz. 42: 
241-264 pis. 7-12. 1906. 
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