58 CARNEGIE INSTITUTION OF WASHINGTON. 



to take a tracing from a fine pen-point, making it possible to divide 

 the millimeters and to read actual changes in size of 0.01 mm. or 0.0004 

 inch. The lever set is supported on a rack-and-pinion column with a 

 vertical movement of 10 cm. and the clock may be adjusted at any 

 height on a fixed vertical column by a sleeved arm and set-screw. A 

 dozen of these instruments have been constructed and used in getting 

 the accompanying results on growth. 



Growth of Eriogonum in relation to Light, Temperature, and Transpiration, 



hy Francis E. Lloyd. 



It was mentioned in a previous report (Carnegie Institution Year 

 Book for 1912, p. 61), that in Eriogonum nudum the transpiration- 

 rates and growth stand in reverse relation to each other, the magni- 

 tudes of water-loss being sufficient to produce a checking of growth or 

 even shrinkage of volume of the growing parts. It was inferred that 

 this checking of growth was the direct result of net water-loss, and not 

 of supposed inhibiting effect of light upon growth, a doctrine which 

 has been passively accepted for many years. During the present 

 season opportunity has presented itself for a more careful study of the 

 behavior of the plant in question, which, on account of its long, slender, 

 naked internodes, suppUes a pecuharly good object for investigation. 

 This was carried on by methods of field auxanometry, the apparatus 

 being so arranged that the growing portion under observation could 

 be inclosed within a chamber in such manner that humidity, both 

 quality and quantity of light, and, to a large extent, temperature also, 

 could be controlled. 



The average rates of growth during the daylight periods were found 

 to be usually greater and only occasionally less than in the periods of 

 darkness, depending upon the state of the growing part, temperature, 

 humidity, or the amount of water available for that part. 



The daily march of growth is as follows : During the early daylight 

 hours until about 8 there is usually a slight rise in growth-rate. After 

 that hour the rate falls to a low value, or, much more frequently, there 

 ensues an actual shrinkage. This is the period during which the loss 

 of water by transpiration is rapidly increasing, reaching its mxaximum 

 at about noon. Coincidentally with the checking of transpiration, 

 the growth-rates rapidly increase in value, the maximum rate being 

 attained by 1 or 2 p. m., and thereafter mamtained, with fluctuations, 

 until 6 p. m., when the rates fall to the night values. The afternoon 

 rates are great enough to more than make up for the negative behavior 

 of the morning, except, as above stated, under unusual conditions. 



That fight can not be held to account for the retardation of growth 

 during the morning hours as above indicated has been shown to be 

 an untenable view, since it was found possible experimentally to alter 

 the rates both positively and negatively quite independently of the 



