148 GROWTH. [CH. VI 



(188) Light. 



Vines^ has shown that light has a retarding effect on 

 the growth of Phycomyces. A ripe sporangium is allowed 

 to burst in a watch-glass of water and a few drops are 

 placed, by means of a needle, on a thick slice of bread, 

 which should be previously steamed to roughly sterilise it. 

 When the fungus begins to appear, a glass plate pierced 

 by holes is laid on the bread and through these hyphse 

 grow ; in this way hyphae sufficiently isolated for observa- 

 tion are obtained. The bread is placed in a saucer 

 containing a little water and covered with a flat- sided 

 glass cover. It is now placed on an apparatus by which it 

 is kept revolving once in 30 minutes on a vertical axis, so 

 as to avoid heliotropic curvatures'". If the hyphse are 

 growing vigorously readings may be taken every 15 

 minutes for an hour, and afterwards at intervals of 30 

 minutes. When sufficient readings have been taken to 

 get a record of the course of the growth-rate, i,e. to 

 ascertain whether the rate is steady, or increasing or 

 decreasing, the culture is darkened by a thick cardboard 

 coyer placed over the glass. The rotation should be 

 continued and temperatures taken by a thermometer 

 whose bulb is inside the glass vessel covering the fungus. 

 It is a good plan to wet the cardboard cover on the 

 outside, so that the temperature during the dark period 

 may be slightly cooler than during the period of illu- 

 mination. After half-an-hour or an hour the dark cover 



' Sachs' Arheiten, ii. p. 133. 



' We use a drum turning on a strong steel axis and driven by an 

 endless band connected with a pulley driven by clockwork. 



