Cultures 143 



CULTURES. It is often very desirable to be able to cultivate Green Algae 

 after they have been removed from their natural surroundings. In this way 

 it is sometimes possible, by the exercise of due care, to obtain an insight into 

 phases of their life-history which have previously been very obscure. The 

 Algae should be grown as nearly as possible under natural conditions, and 

 filtered rain-water or tap-water may be used for some of the coarser kinds, 

 which also require a considerable volume of water. Filtered water from 

 Sphagnum-bogs is most useful as a medium in which to grow numerous Green 

 Algae normally occurring in stagnant situations. 



In some cases, more particularly for experimental purposes, it is desirable 

 to use a nutritive medium containing rather more of the available raw food- 

 materials than is to be found in a natural medium. It is, however, necessary 

 from the very outset to warn the investigator that many of the Green Algae 

 are very plastic organisms, and if the conditions of the culture are to a large 

 extent abnormal (as compared with natural conditions), it is more than likely 

 that strange phases and monstrous forms will be obtained, such as seldom if 

 ever occur in nature. At the same time, it must be observed that a strange 

 phase arising under abnormal conditions of culture may sometimes afford 

 valuable evidence concerning phylogenetic relationships. 



To obtain successful cultures, therefore, it is necessary that the conditions 

 be as natural as possible, otherwise the development of monstrous forms will 

 tend to lessen the value of the results obtained. 



Most of the purely aquatic forms of the Chlorophyceae can be cultivated in 

 distilled water to which a small quantity of some nutritive solution has been 

 added. For the smaller species the vessels used may be Petri dishes, test- 

 tubes plugged with cotton-wool, or better still, circular glass boxes with glass 

 lids; but large Algae, such as Spirogyra, (Edogonium, etc., are best given a 

 large volume of water, preferably one or two gallons. The culture-vessels 

 should be placed in a north window or in such a situation that they are never 

 exposed to direct sunlight. Temperature is also one of the most important 

 factors. Ordinary room and laboratory temperatures are in most cases rapidly 

 fatal, and the culture-vessels are best kept in chambers the lower parts of 

 which are lined with zinc, and through which cold tap- water can, if necessary, 

 be kept constantly running. 



There are a number of well-known culture solutions, all of which require to be used in 

 a very dilute state. Some of them are as follows : 



Knop's solution \ Water 1000 grammes ; 0'25 gr. of MgS0 4 ; 1 gr. of Ca (N0 3 ) 2 ; 0'25 gr. 

 of KH 2 PO 4 ; 0-12 gr. of KC1 ; and a trace of Fe 2 Cl G . This makes a strength of 0'172 per 

 cent., which is about the right strength for ordinary purposes. Other strengths can be 

 made according to requirements. 



Klebs' solution : 4 parts of Ca (N0 3 ) 2 ; 1 part KH 2 P0 4 ; 1 part of KN0 3 ; 1 part 

 MgS0 4 ; made up in strengths from 0*2 to 1 per cent. 



