612 PHYSIOLOGY. 



necessarily of relatively little value, since it by no means represents what 

 happens under natural circumstances. 



K,au wenh off, whose paper on this subject is the most complete, and 

 which contains references to the literature of the subject, shows that the 

 day and night growth is variable in different species, that what holds good 

 in one does not do so for another ; and this agrees with the result of 

 Lindley's experiments, in the Transactions of the Horticultural Society 

 of London, new ser. vol. iii. p. 101. 



Measurement of Rate of Growth. For purposes where great accuracy is 

 not required, marks made upon the growing stem at regular distances apart, 

 or a measuring-rod placed in juxtaposition, are sufficient ; but where great 

 accuracy and the measurement of minute spaces are demanded, recourse 

 must be had to special instruments called Auxanometers. In the simplest 

 form of this instrument a thread is attached to the growing plant, the 

 other end of the thread being carried over pulleys and moving an index 

 attached to a scale. Self-registering growth-measurers present many ad- 

 vantages. In these the rate of growth is marked by an index attached 

 by a thread to the plant, and travelling over a blackened cj'linder revolving 

 by clockwork in fixed periods of time, and on which the indications of 

 the index are traced. 



Alternations of Growth. In addition to periodic or rhythmic waves 

 of growth, a sort of compensatory growth is often observed ; so that if 

 growth be active in one organ, it is relatively passive in another, and vice 

 versa. If one organ be hypertrophied or inordinately developed, it often 

 happens that another is correspondingly restricted. The operation of this 

 law of compensation is particularly evident in many cases of monstrosity. 

 It may also be easily observed in the case of many Conifers, e. g. in Araucaria 

 imbricata or Abies Nordmanniana, where in one season the growth of the 

 terminal shoot exceeds that of the lateral subverticillate ones beneath it, 

 while in another season the lateral shoots grow faster than the terminal 

 one. 



Force exerted during Growth, The force with which fluids ascend in 

 the stem has been repeatedly measured from the time of Hales ; but the 

 actual force exerted by the mass of growing tissues has not been so fre- 

 quently made the subject of accurate measurements. It is common to see 

 stones uplifted by trees in their growth, and paving-stones raised by the 

 growth of Fungi beneath them. Clark has subjected to measurement a 

 growing fruit of a Pumpkin, which from raising weights of 50-60 lb., 

 finished by raising one of 5000 lb., its own weight being 47 lb. The 

 growth of the roots of this plant was estimated at 1000 feet a day. This 

 is no doubt an extreme case, but it may suffice to illustrate the enormous 

 force exerted by plants in their growth. 



