1896, ] Aqueous Media for Preserving Alge. 141 
tion of picric acid and preserving in strong alcohol is a very 
good one, especially for specimens to be imbedded in paraffin 
or for special work in connection with particular problems. 
Better still is fixing in some special solution such as a satu- 
rated solution of picric acid, 0. 5—1 per cent. chromic acid, Per- 
enyis fluid, Hermann’s mixture, etc., and transferring through 
the ordinary grades of alcohol, or by dialysis, up to 70 per 
cent. strength and preserving in that. 
Such material is in excellent condition for imbedding in 
paraffin or celloidin, but for the ordinary class work, for man- 
ipulation by the student himself, the specimens must gener- 
y be transferred again to water. 
ut the preparation by these methods of material fora large 
class is often a considerable task. The more delicate forms 
too are seldom in a thoroughly satisfactory condition. 
It has been found to faciliate the class-work on all the 
‘typtogams very much to use freezing methods in the prepar- 
ation of sections for the class, and either to have the sections 
Cut by an assistant or by different members of the class at dif- 
ferent times. A description of a convenient freezing device 
and methods of imbedding in aqueous media will be published 
by one of us in the next number of this journal. 
ue methods and the preservation of natural form and 
: 0 the different parts with as little change as possible have 
endered it very desirable that aqueous media be employed if 
Possible for Preserving fluids. 
ber of fluids have been subject to experiment by the 
ers that these notes of their experience, while con- 
oes ing especially new, may serve as useful-hints to 
Chrome alum. 
Minar... ec’ ~Was used by Guignard? for fixing various 
and ic for the Purpose of investigating the structure 
tested se oPment of the mucilage ducts. Later it has been 
at the Biological Station at Helgoland by Lotsy? upon 
"Ann. Sei 
2 - Nat., Bot. VII. 15: 1-46 
Bot. Centralblatt 60: 15-16. 1894, = 
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