14 
G. F. Atkinson, 
of the pileus and forming an annulus on the stem”. In bis figure of the 
morphology of Agaricus campestris (1. c. fig. 42) he shows a universal 
veil (U. V.) extending from the base of the stem over the entire fruit 
body. Düring the expansion of the plant this universal veil is ruptured 
and the lower part is shown as a small ring at the base of the stem. 
But the interpretation of bis concept of universal veil and annulus is 
made difficult by the illustration of an additional structure, the inner, or 
partial veil which appears higher up on the stem and is marked annulus 
(AN). In bis description of the family Agaricaceae (1. c. p. 11) he 
clearly distinguishes between the “primary” or “universal veil” which 
forms the volva and fragments on the pileus, and the partial veil by the 
Statement, “In some species a secondary or partial veil is also 
present in the earlier stages spreading from the upper part of the stem 
to the edge of the pileus. This veil is finally ruptured and partly persists 
as a ring or annulus (A) encircling the stem”. 
Such an interpretation of the morphology of Agaricus campestris 
is certainly far from lucid. One of the very confusing features in all 
systematic works on the Agaricaceae is the use of the term veil, and 
“universal veil”. I must confess that I have never been quite able 
to form a satisfactory concept of the use of tliese terms, and have always 
met with difficulty in attempting an explanation of them to my students. 
But after a study of the development of several species of Agaricus , of 
Amanitopsis vaginata and Lepiota clypeolaria , I believe it is possible to 
obtain a clearer insight into the homologies of tliese structures than we 
have had heretofore. But caution should be used in attempting to apply 
these interpretations to all of the Agaricaceae. We need careful studies 
of development in all of the genera to determine the origin and diffe- 
rentiation of the “universal veils”, and other sections of the genus Lepiota 
than that to which L. clypeolaria belongs should be studied. 
“Universal veil” in Lepiota clypeolaria. 
In Lepiota clypeolaria there is a well formed external layer sur- 
rounding the very young fruit body before there is any internal differen- 
tiation of the fundamental parts of the fruit body in the center of the 
primordium. This may well be regarded as a “universal veil”, for at 
later stages it envelops the stem, is continuous over the pileus and 
remains concrete with it. The development of Lepiota clypeolaria will 
be described in another paper. A similar “universal veil” is present in 
the very young stages of Armillaria mellea 4 ), but its inner zone is not 
quite so well organized as in that of Lepiota clypeolaria. 
Differentiation of the primordia in Agaricus arvensis. 
I have recently described the development of Agaricus arvensis and 
A. comtulus 5 ) from material collected in the forests of the Jura Moun¬ 
tains, near Pontarlier, France, in 1905. Different stages of the very young 
4) Atkinson, Geo. F., The development of Armillaria mellea. Myc. 
Centralbl. 4, 113—121, 1914. 
5) Atkinson, Geo. F., The development of Agaricus arvensis and 
A. comtulus. Am. Journ. Bot. 1, 3—22; pls. 1, 2, 1914. 
