DIV. II 



PHYSIOLOGY 



279 



meter is shown. The thread fastened to the top of the plant to be observed 

 is passed over the movable pulley (r) and held taut by the weight (g), which 

 should not be so heavy as to exert any strain on the plant. To the pulley there 

 is attached a slender pointer (z), which is twenty times as long as the radius 

 of the pulley, and this indicates on the scale (S) the rapidity of the growth 

 magnified twenty-fold. 



Self -registering auxanometers are also used, especially in making extended 

 observations. In Fig. 255, at the right, is shown one of simple construction. 

 The radius of the wheel (-ft) corresponds to the long arm, and the radius of the 

 small wheel (?) to the short arm of the lever, in the preceding apparatus. Any 

 movement of the wheel, induced by the elongation of the shoot, and the con- 

 sequent descent of the weight (</), is recorded on the revolving drum (CO by the 

 pointer attached to the weight Z, which is in turn balanced by the counter- weight 



FIG. 255. Simple and self-registering auxanometers. For description see text. 



( IV]. The drum is covered with smoked paper, and kept in rotation by the clock- 

 work (U). If the drum is set so that it rotates on its axis once every hour, the 

 perpendicular distances between the tracings on the drum will indicate the propor- 

 tional hourly growth. 



The rate of growth in plants is usually too slow to allow of the 

 result being directly observed after a short time. Only some fungal 

 hyphae and the stamens of some Gramineae grow so rapidly that 

 their elongation is evident, even to the naked eye. The fructifica- 

 tion of the Gasteromycetous fungus Didyophora grows in length to the 

 extent of 5 mm. per minute (A. MOLLER), and according to AsKENASY 

 an increase in length of T8 mm. a minute has been observed in 

 the stamens of Triticum (Wheat). This approximately corresponds to 

 the rate of movement of the minute-hand of a watch. In comparison 

 with these the next most rapidly-growing organ known is the leaf- 



