54 OF THE DESMIDIACE.E AND SIMILAR MINUTE ALG.E. 



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 

 irom the method of employing them. Following a natural 

 law, the frustule, immediately upon being enclosed in its 

 cell, begins to part with the water contained within itself. 

 And what is the consequence ? The surrounding medium 

 cannot take the place of the water, the primordial 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 Schlauch of the Germans), is 

 the name given by Mohl to the delicate membrane which lines the 

 inner cell wall, and which encloses the protoplasm, or viscid fluid, 

 with granules intermixed, which forms the contents of the cell. — Ed. 



