392 MANIPULATION. 



as may be required. The larger species of Euastrum, Micras- 

 terias, Closterium, &c., are generally situated at the bottom 

 of the pool, either spread out as a thin gelatinous stratum, or 

 coUected into finger-like tufts. If the finger be gently passed 

 beneath them, they wiU rise to the surface in little masses, 

 and with care may be removed and strained through the linen, 

 leaving only a mere stain or a little dirt; but by repeated 

 fiUings up and strainings a considerable quantity wUl be 

 obtained. If not very gelatinous, the water passes freely 

 through the linen, from which the specimen can be scraped 

 with a knife and transferred to a smaller piece ; but in many 

 species the fluid at length does not admit of being strained off 

 without the employment of such force as would cause the 

 fronds also to pass through, and in this case it should be 

 poured into bottles until they are quite full. But many 

 species of Staurastnun, Pediastrum, &c., usually form a 

 greenish or dirty cloud upon the stems and leaves of the 

 fihform aquatic plants, and to collect them requires more care 

 than is necessary in the former instances. In this state, the 

 slightest touch will break up the whole mass and disperse it 

 through the water. I would recommend the following method 

 as the best adapted for securing them: — ^Let the hand be 

 passed very gently into the water and beneath the cloud, the 

 palm upwards and the fingers apart, so that the leaves or stem 

 of the invested plant may he between them and as near the 

 palm as possible ; then close the fingers, and, keeping the hand 

 in the same position, but concave, draw it cautiously towards 

 the surface, when, if the plant has been allowed to slip easily 

 and with an equable movement through the fingers, the 

 Desmidieae, in this way brushed off, will be found lying in the 

 palm. The greatest difficulty is in withdrawing the hand 

 from the surface of the water, and probably but little will be 

 retained at first; practice, however, wiU soon render the 

 -operation easy and successful. The contents of the hand 

 should be transferred at once either to a bottle, or, in case 

 much water has been taken up, into the box, which must be 

 close at hand, and when this is full it can be emptied on the 

 linen as before. But in this case the hnen should be pressed 



