28 H^MATOCOCCUS LESS. 



that of Hgematococcus, on the other hand, is formed of a 

 carbohydrate called cellulose, allied in composition to 

 starch, sugar, and gum, and having the formula C 6 H 10 O 5 . 

 Many vegetable substances, such as cotton, consist of 

 cellulose, and wood is a modification of the same com- 

 pound. Cellulose is stained yellow by iodine, but iodine 

 and sulphuric acid together turn it blue, and a similar 

 colour is produced by a solution of iodine and potassium 

 iodide in zinc chloride known as Schulze's solution. These 

 tests are quite easily applied to Haematococcus : the proto- 

 plasm stains a deep yellowish-brown, around which is seen 

 a sort of blue cloud due to the stained and partly-dissolved 

 cell-wall. 



It has been stated that in stagnant water in which it has 

 been cultivated for a length of time Haematococcus some- 

 times assumes an amoeboid form. In any case, after leading 

 an active existence for a longer or shorter time it comes to 

 rest, loses its flagella, and throws around itself a thick cell- 

 wall of cellulose (Fig. 3, B), thus becoming encysted. So 

 that, as in Amoeba, there is an alternation of an active 

 or motile with a stationary or resting condition. 



In the matter of nutrition the differences between Haema- 

 tococcus and Amoeba are very marked and indeed funda- 

 mental. As we have seen, Haematococcus has no pseudopods, 

 and therefore cannot take in solid food after the manner 

 of Amosba : moreover, even in its active condition it is 

 usually surrounded by an imperforate cell-wall, which of 

 course quite precludes the possibility of ingestion. As a 

 matter of observation, also, however long it is watched it is 

 never seen to feed in the ordinary sense of the word. Never- 

 theless it must take in food in some way or other, or the de- 

 composition of its protoplasm would soon bring it to an end. 



