VIII PREFACE, 
the deserts of Lower California. Of special interest is the unique 
fruiting habit of Gongylocarpus and Burragea, which bear their cap- 
sules embedded in the wood of the flowering branches. 
The two short papers forming part 13 are studies by Mr. Ivar Tide- 
strom, of the Bureau of Plant Industry, United States Department 
of Agriculture, of plants in which he has become jnterested., These 
are considered with reference both to their nomenclatorial history and 
to their botanical characters. The first paper relates to a well-known 
fern type, the forms of which are regarded by the author as composing 
two species. The second treats of two tropical and subtropical weeds 
which have found their way into the southern United States. 
In the final paper Mr. Edward A, Goldman puts on record the 
the botanical results of a biological exploration in Lower California, 
which was carried out in 1905 and 1906 by Mr. E. W. Nelson and 
himself, as members of the staff of the Bureau of Biological Survey, 
United States Department of Agriculture. The paper consists pri- 
marily of a list of the plants collected, with notes on distribution , to 
which are added descriptive ecological and economic data and tech- 
nical descriptions of three new species of oak. A limited use has been 
made of the collections and records of others. ‘This paper adds mate- 
rially to our knowledge of an extensive flora, very interesting in its 
adaptations to diversified conditions of latitude, altitude, and rainfall. 
Frepericx V. Covi, 
Curator of the United States National Herbarium. 
