APPARATUS FOR MEASURING GROWTH. 



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that in the case of Phycomyces nilens (Fig. 3, p. 5) one of the Mucors already so 

 often mentioned, and a plant not only devoid of chlorophyll but also a non-cellular 

 one, a direct action of light on the 

 rapidity of growth occurs of such a 

 kind that even light of feeble intensity 

 causes a retardation of the growth in 

 the course of a single hour, while a 

 similarly short period of darkness ac- 

 celerates it. Here also, just as in the 

 case of the highly organised plants, 

 it is the more refrangible rays of the 

 light, the blue and violet, which retard 

 the growth — a point to which I have 

 already expressly referred — while it is 

 chiefly the less refrangible rays, the 

 yellow, which cause assimilation in the 

 chlorophyll. Since this is a very im- 

 portant point in vegetable physiology, 

 I may take this opportunity of describ- 

 ing the apparatus which I have con- 

 structed for the purpose of such measure- 

 ments of growth on small and simple 

 plants, and with which Vines made 

 his observations. The apparatus here 

 figured (Fig. 350), although constructed 

 on exactly the same principle, is still 

 more convenient. On a very strong, 

 firm, wooden tripod, a thick slab is 

 arranged by means of the triangular 

 prismatic foot A, so that it can be 

 moved vertically and fixed. On the 

 slab stands a very firm cathetometer 

 E, the horizontal telescope of which 

 affords an enlargement of about fifteen 

 diameters, at 12-20 centimeters focal 

 distance. The apparatus ^ is a very 

 strong and carefully constructed clock- 

 work, which is for the purpose of allow- 

 ing a vertical axis which supports a 

 horizontal brass plate to make exactly 

 one revolution in an hour. On this 

 plate is placed the plant to be ob- 

 served, in our case, for instance, a 

 Phycomyces bearing sporangia, D, which 

 grows on a piece of bread, and is covered with a glass bell-jar C. The telescope of 

 the cathetometer, which contains a micrometer scale on which c i mm. can be read 

 [3] 00 



Fig. 350. — Apparatus for measuring the growth in 

 teugth of small plants {D) by means of the cathetometer 



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