54 OF THE DESMIDIACE^E AND SIMILAR MINUTE ALGA;. 
Spirogyra), whose characters depend entirely on the arrange- 
ment of the cell contents, are destroyed in the act of drying, 
their structure is utterly lost, and no soaking in water will 
ever restore them. It happens too, sometimes, that we have 
only a poor supply of some rare species, which gradually 
disappears under too frequent examinations, and its pos- 
sessor would gladly preserve the remainder once and for all. 
Influenced by these considerations, physiologists have 
applied themselves, from time to time, to the discovery of 
some method by which these minute and delicate organisms 
may be kept unchanged for a lengthened period ; but it 
must be confessed, with less success than their industry has 
merited. 
The great want which has marred all their efforts has 
been a fitting medium ; or, in other words, a fluid of such 
a nature that the plant, when immersed in it, shall not 
become distorted, or indeed receive any appreciable change 
for a long lapse of years, provided the cement enclosing it 
retains its air-tight properties. The want of success, it 
must be allowed, has not arisen from the positive evapora- 
tion of the liquids employed (glycerine, chloride of cal- 
cium, &c. retain their density for a very long time), but 
from the method of employing them. Following a natural 
law, the frustule, immediately upon being enclosed in its 
cell, begins to part Avith the Avater contained Avithin itself. 
And Avhat is the consequence ? The surrounding medium 
cannot take the place of the water, the jxrimordial utricle* 
contracts, the contents of the cell collapse, and the plant is 
left as much changed and disfigured as though it had been 
originally dried. 
The botanical world is, therefore, greatly indebted to 
Herr Hantzsch, of Dresden, for his researches in this direc- 
tion, which have resulted in discovering an arrangement 
* The primordial utricle (primordial Schlmich of the Germans), is- 
the name given by Mohl to the delicate membrane Avhich lines the 
inner cell Avail, and which encloses the protoplasm, or viscid fluid* 
with granules intermixed, which forms the contents of the cell. — E d. 
