4i6 PROrOPHYTA 



condition in the form of resting-spores, which may become dried up and 

 retain their vitahty for years as a dry powder, resuming their activity when 

 again placed in water. McNab (Ann. tv: Mag. Nat. Hist., 1883, p. 124) 

 has, by the use of osmic acid and carmine, detected a nucleus in the 

 free ciliated state of Protococcus, and also in individuals in which cell- 

 division is going on. 



When in an active condition in sunlight, Protococcus gives off into 

 the surrounding water large quantities of oxygen, the result of the activity 

 of its chlorophyll, thus contributing to render it habitable for animal 

 life. The amount of the red pigment varies greatly. It is often con- 

 fined to a small spot near to the point of attachment of the cilia, the 

 'pigment-spot,' bearing a close resemblance to the 'eye-spot' of the 

 Flagellate Infusoria. If present in larger quantities, so as to give a red 

 tint to the entire organism, this is known as Hoematococcus (Ag.). In 

 the palmella-condition this form frequently presents the structure and 

 appearance of a blood-red incrustation on rocks and stones, when it has 

 been described as Palmella cruenta (Ag.) and Porphyridium cruentum 

 (Nag.). Very closely allied are the Palmella prodigiosa (Mont.) (Monas 

 prodigiosa, Ehrb.), which forms blood-red spots on bread, potatoes, &c., 

 and the Palmella nivalis (Hook.) (Protococcus nivalis, Ag., Chlamydo- 

 coccus nivahs, A. Br.), which, under the name of 'red snow,' frequently 

 covers large tracts of snow in arctic and alpine regions in a very short time. 

 Phipson (Compt. Rend., Ixxxix., 1879, pp 316, 1078) has examined 

 the red colouring-matter of Palmella cruenta, and finds it to consist of 

 minute globules about four microns ('004 mm.) in diameter, closely 

 resembling those of the haemaglobin of blood, but somewhat smaller. 

 He proposes for the pigment the name pabnellin. It is soluble in 

 water, but insoluble in alcohol, ether, and carbon bisulphide. Like 

 hsemaglobin it contains traces of iron. Other lowly-organised snow and 

 ice plants besides Palmella nivalis are brightly coloured, and appear to 

 perform an important function in melting the snow by their strong 

 absorption of the rays of heat. In addition to palmellin, Palmella 

 contains also xanthophyll, and a small quantity of another substance of 

 the nature of camphor and possessing a marshy odour, which Phipson 

 calls characin, and which is present in other terrestrial and fresh-water 

 algae, and espiecially in Chara. In the haematococcus-condition it is 

 sometimes impossible to detect directly the presence of chlorophyll ; but 

 experiments by Engelmann (Rev. Internat. Sci. Biol, 1882, p. 468, and 

 Bot. Zeit., 1882, p. 663) seem to show that there is always a certain 

 amount of chlorophyll present, though it is possible that the power 

 which Hsematococcus undoubtedly has of decomposing carbon dioxide 

 may be due to the presence of other substances allied to chlorophyll, 

 but differing from it in colour. 



