144 Chlorophycex 



Artari's solution: Water 100 grammes; 0'25 gr. of NH 4 N0 3 ; O'l gr. of KH 2 P0 4 ; 

 0-025 gr. of MgS0 4 ; and trace of Fe 2 Cl 6 . 



Beijerinctts solution : Water 100 grammes ; 0'05 gr. of NH 4 N0 3 ; 0'02 gr. of KH 2 P0 4 ; 

 0-02 gr. of MgS0 4 ; O'Ol gr. of CaCl 2 ; and trace of FeS0 4 . 



Knop's solution in varying strengths, but always weak, gives very satisfactory results ; 

 and if greater concentrations are desired, the strength of the solution should be very 

 gradually increased. 



Many of the subaerial Chlorophycese, such as Stichococcus, Coccomyxa, etc., can be 

 cultivated on sterilized plates of porcelain or plaster of Paris which have been saturated 

 with the weak culture solution. Sterilized porous pots of soil may also be used for the 

 terrestrial species of Vaucheria. 



Marshall Ward ('99) used a mixture of the prepared culture solution and silica jelly, 

 both of which were sterilized and poured into glass dishes. 



It is sometimes desirable, especially if pure cultures are required, to begin with one or 

 two individuals. These can be isolated, and placed either in a hanging-drop or in a small 

 cell on an ordinary slide, the cell being constantly supplied with the culture solution by 

 means of blotting-paper strips. Cultures of this kind, which it is often necessary to keep 

 for a long time, are very liable to become infested with Bacteria and Fungi. This can be 

 prevented without any detriment to the Algse, by the addition of 0'05 per cent, of neutral 

 potassium chromate to the culture fluid, as recommended by Klebs, or by the addition of 

 O'Ol per cent, of potassium bichromate, which Palla states to be quite as efficacious. 



Many Algee grow excellently in a fluid consisting only of filtered sterilized water 

 obtained from the pools or bogs in which they were growing naturally. 



Solid media, for very obvious reasons, do not give good results, and very often merely 

 induce the formation of monstrosities and abnormal states. Agar-agar is rather better 

 than gelatin, especially if it be dissolved in 0'2 per cent. Knop's solution. Some few of 

 the Protococcales and some of the Green Flagellates can be cultivated on this medium, 

 but such results as are obtained are not often of much value 1 . 



Some of the Protococcales of the plankton can be cultivated by using the filtered water 

 from a boiled plankton-catch, or by using the sterilized filtrate from a plankton -catch a 

 few days old. 



The Conjugatse are decidedly difficult Algse to cultivate, and it is soon found that the 

 conditions of culture suitable for one species are often a complete failure in the case of 

 another. Desmids thrive best in filtered water from upland Sphagnum-bogs. In some of 

 the Zygnemaceee conjugation can sometimes be hastened by exposing to sunlight, and also 

 by placing in a 2 4 per cent, solution of maltose or saccharose. The same result may be 

 obtained by first putting the Alga into weak Knop's solution (not more than 0'2per cent.) 

 for about a week and then transferring to distilled water. 



As a general rule, cultures of the Green Algae thrive best when exposed to diffuse 

 daylight. In cultures under coloured light, Dangeard ('09) has shown that Chlorella 

 develops best in red and orange light, feebly in violet and not at all in green light. 

 Changes in intensity of light, from diffuse light to darkness or vice versa, sometimes 

 promote the formation of zoogonidia, as may also changes in the composition of the 

 culture solution. 



1 The author has obtained normal cultures of Ulothrix subtilis and of two species of 

 Cosmarimn on agar-agar dissolved in 0-2 per cent. Knop's solution. 



For the most recent work on the culture of certain forms of Green Alga on solid media consult 

 Kufferath ('13) and especially Chodat ('13). The last-named author has attempted to split up 

 the widely distributed Alga Scenedesntus qiiadricauda into a number of 'species' on cultural 

 characters. He has also recently described many cultural 'species' of Chlorella. 



