568 Humphrey . — On some 
since (’94) insisted upon the restriction of the ‘ sickle-stage ’ to 
a special phase of sexual cells. Strasburger (’95) has lately 
stated that the nucleolus may be flattened against the nuclear 
wall by the fixing fluid at an early stage of the prophase, 
when the nucleus is, as various observers have pointed out, 
peculiarly sensitive to reagents. Renewed examination of 
a large number of preparations has failed to show me any 
instance of this sort, but there is no reason for doubting that 
such displacement sometimes occurs, though far less com- 
monly than the heaping up of chromatic substance. 
If the so-called 4 sickle-stage ’ bears any relation to the 
passage from sporophyte to gametophyte marked by the 
reduction in the number of chromosomes, as Zimmermann 
believes, it should be found always during the prophase of the 
first division of the definitive pollen- or spore-mother-cell. 
Yet, in the study of a very large number of such cells in the 
very stage indicated, and from several different plants, I have 
been able to find no such sickle-shaped nucleolus, nor indeed 
any nucleolus, in contact with the nuclear membrane. For 
the quick fixation of the nuclear constituents with the least 
possible displacement, the trial of many fluids has led me to 
prefer, in general, the alcoholic to the aqueous media. Of the 
latter, Hermann’s fluid seems oftenest to do well. Merkel’s 
fluid, recommended by Zimmermann, is much less satisfactory. 
But alcohol, sublimate-alcohol, or the fluid recommended for 
some animal tissues by Mann, are the most to be recommended 
for vascular plants, especially for reproductive tissues. As the 
formula for Mann’s fluid has not, to my knowledge, been 
published in a botanical journal, it may be worth while to 
give it here : — 
Absolute alcohol . 
, 
. 
IOO cc. 
Picric acid 
, 
. 
4 grams, 
Corrosive sublimate 
. 
. 
15 „ 
Tannin . 
Dissolve 
and filter. 
7 „ 
While it is, therefore, impossible to say positively what is 
