Notes on Recent Literature. 
377 
An interesting feature of Dr. Graebner’s book is the addition of 
a short account of the animal life of each plant-community, 
contributed by Oberlehrer F. G. Meyer. The work is illustrated by 
a number of text-figures of the habit of characteristic plants 
belonging to the different communities and by a few views of 
vegetation. 
The book would we think have been improved by regular lists 
of species belonging to the various plant-communities with indications 
of dominance, relative abundance, etc. 
The treatment of the effect of humus scarcely brings into 
sufficient prominence the important distinction between “ Milde 
Humus ” and “ Rohhumus,” and we miss also an adequate treatment 
of the problems of succession, without which it is impossible to 
obtain a just conception of the problems of vegetation and of the true 
relationships of the different communities. It is rather on this line, 
together with intensive study, that we must look for an increase in 
the definiteness of our concepts of vegetation units, without which 
we cannot hope to attain to a really natural classification of these 
units. A.G.T. 
NOTES ON RECENT LITERATURE. 
Recent Progress in the Study of the Embryo-Sac 
OF THE AnGIOSPERMS. 
I ^HE female gametophyte of the Angiosperms has long been 
regarded as “ a morphological problem of great obscurity.” 1 
While the monophyletic origin of Angiosperms from a Gymnosper- 
mous stock is now assumed by most authors, 3 the gulf between the 
archegonium-bearing prothallus of a typical Gymnosperm and the 
eight-nucleate and bipolar embryo-sac of the Angiosperm has proved a 
very difficult one to bridge. Among the Gymnosperms, the embryo- 
sac 'of Gnetum, with its egg organised at the free-nuclear stage, 
seemed till recently to offer the nearest approach to Angiosperm 
conditions ; but even here no clue was found to the phylogenetic 
origin of the endosperm in the latter group. The disputed mor¬ 
phology of this tissue has been the great difficulty in interpreting the 
embryo-sac of the Angiosperm ip terms of that of the Gymnosperm. 
Normally, it is formed after fertilisation by the division of a fusion- 
nucleus consisting of the two polar nuclei and a male nucleus 3 — 
and until recently no tissue comparable to this in origin has been 
described in a Gymnosperm. 
Before discussing the light thrown by recent work upon the 
phylogeny of the embryo-sac, it may be of interest to touch briefly 
on some of the principal suggestions that have been advanced to 
account for its homologies and possible origin. Strasburger in 
1879 suggested* that the eight nuclei in the embryo-sac represent 
1 Coulter and Chamberlain (03), p. 88. 
2 See, however, Campbell, “ Evolution of Plants,” 1899, p. 155, 
and “Mosses and Ferns, 1905, p. 605; also Coulter and 
Chamberlain, 1904, pp. 283-287. 
Sargant 1908, p. 126. 4 Strasburger 1879, pp. 137-139. 
