340 THE AMERICAN NATURALIST.  [VoL. XXXIII. 
a very complete study. From the large amount of valuable matter 
a few points of especial interest may be selected. 
After discussing the economic importance of the question, the 
structure of nematode worms and the symptoms of their attack, there 
follows a careful description of the root-gall, in which it is shown that 
the worms affect the plants, not directly by extracting nutriment, but 
indirectly by modifying the structure of the root so that the flow of 
sap is interfered with, and secondarily by weakening it so that it is 
more susceptible to other diseases. The structure and development 
of Heterodera, the gall nematode, are fully described; and in connec- 
tion with a careful review of the literature the authors maintain the 
identity of the German species with that found by Cobb in Australia, 
that studied by Neal and Atkinson in the southern United States, and 
that on which they worked themselves in Massachusetts. Although 
carefully reached, the conclusion is still open to question. The 
nematodes display great uniformity in general structure, and species 
are at best often very difficult to distinguish. It is not clear that the 
lips, together with the oral and caudal papillz, were examined in all 
these forms; but these are the characters at present accepted as the 
most reliable for specific determination. And while specimens of the 
German form were compared with the Massachusetts variety, it was 
only the female, while on the analogy of other species in this group the 
male alone would suffice for specific determination. Furthermore, in 
some points at least, the habits of the two forms are not in agreement, 
so that the specific identity can hardly be regarded as established. 
The authors have discussed very completely the various methods’ 
of treatment for nematode root-galls, and have experimented in detail 
with most of them. They reach the conclusion that “the most effec- 
tual, complete, and practical method of exterminating nematodes in 
greenhouses is by heating the soil by means of steam,” which is 
both comparatively inexpensive and noticeably beneficial to the soil. 
While experimenting they noticed the comparative indifference of 
ffeterodera to an atmosphere strong in CO. This is interesting as 
confirming for one free living representative of the group what Bunge 
long ago demonstrated for certain parasitic species. The paper is 
well illustrated and of permanent value. 
2. A good résumé of present knowledge on the nematodes has 
recently appeared in the form of a somewhat popular article,’ which 
1 Cobb, N. A. Extract from Manuscript Report on the Parasites of Stock, 
Miscell. Publ. Dept. of Agr. Sidney, N.S.W., No. 215; also from Agr. Gazette 
N. S. W. (March and April, 1898), 62 pp., 129 text-figures. 
