376 General Notes. [April 
Fe are to each other as 72:56, Mg is in excess, and the substance 
crystallizes as does MgSo,+ 7H,O. In compounds containing 
less Mg (as 2MgSo,-+ FeSo,) + 7H,0O, the proportions of Mg 
and Fe are as 48: 56, and the crystallization is that of melanterite. 
Various conditions effect the crystallization of mixed bodies, but 
the most important of these, according to Schrauf’s opinion, is 
the one mentioned above. If this law is found to be general in 
its application, the present views in regard to the dimorphism of 
many compounds belonging to the so-called iso-dimorphous 
groups will have to be modified. 
BOTANY. 
Botanical Manuals for Students.—Nowadays we are urging 
students to collect and study plants from all the great groups, 
and thereby to familiarize themselves with the vegetable kingdom 
as a whole, but perhaps we too often overlook the difficulties 
which lie before them. Not the least of these is the want of sys- 
tematic manuals in which descriptions of the genera and species 
may be found. It is all very well to tell a student that the name 
and technical description are of much less importance than is the 
knowledge of structure and habits. It is true, no doubt, but, for 
all that, there is need of such works in every laboratory, to serve 
as guides, if for no other purpose. Unfortunately for the Amer- 
ican student, we are as yet poorly supplied with descriptive man- 
uals. In the following list I have enumerated the classes (and 
in some cases the orders under the classes) of the several great 
branches of the plant kingdom, giving for each the name of a useful 
systematic manual. I have not attempted to make a list of the 
works of this kind which are absolutely the best, for too often such 
works are too expensive for the limited means of the botanical 
departments of many schools and colleges. 
PROTOPHYTA. 
Myxomycetes.—Cooke’s Myxomycetes of Great Britain. 
ScHIZOMYCETES.—Grove’s Bacteria and Yeast Fungi. 
CyanopHycE2.—* Cooke’s British Fresh-Water Algz, pp. 203- 
282, and, doubtfully, pp. 1-30. 
ZYGOPHYTA. 
ZoosPOREH.—Cooke’s ai Fresh-Water Algz, pp. 67 (Pando- - 
; rina), 3 hr gh at an ge seh 135-145 (Con- 
fe st Bo oe Farlow w England Alga, 
pp. 41-44 (Ulvacee), ad és (Phzosporez). 
* Edited by Prof. Cuar.es E. Brssry Lincoln, Nebraska. 
year the work on the “ Fresh-Water a of North America,” fs 
p li, ay th eect When that appears it should be substituted fi 
“ British Fresh-Water Algæ” wherever the latter occurs in this list. 
