LIMITING FACTORS TO GROWTH MEASUREMENTS. 339 



by a half-metro scale at the successive observations. Suc- 

 cessive measurements of the same shoot at the same time did 

 not differ by more than ■ 05 cms. , which may be taken as the 

 limit of error for the method. This error is much more con- 

 siderable than in the previous cases, because, although the 

 growth is rapid for this class of plant, yet it is by no means 

 so rapid as the growth of Agave or Dendrocalamus, and thus 

 the error of the method becomes of greater importance. The 

 curves represent however the growth of more shoots than one, 

 and thus the errors will probably average out, and also when 

 a continuous series of measurements is taken at fairly close 

 intervals the general curve may be taken as more accurate 

 than any one of the readings. 



Results. 

 Plate 25 shows the curve of the growth in mm. per two hours 

 of two shoots of Capparis Roxburghii from January 9th, 9 a.m. , 

 to January 11th, 7 a.m. It will be seen that during the day 

 the growth is slow so that either the lowered humidity or the 

 light checks the growth. It is to be observed that there is a 

 contraction of considerable amount in the hotter part of the 

 day when the sun is fully on the plants followed by rapid 

 growth as darkness sets in. It is clear that the water supply 

 is the limiting factor during the'day. Does it continue so 

 during the night ? The night, January 10th to 11th, is an in- 

 teresting reply to this question. The humidity curve rises 

 steadily through the night, while the curve of temperature 

 as steadily falls. The light factor being absent, the case would 

 appear to be a decisive test as to which is the limiting factor 

 through the night. The curve of growth, it will be seen, goes 

 on the whole steadily downward parallel to the curve of tem- 

 perature and shows no tendency whatever to rise in response 

 to the increase of humidity as night advances. A similar 

 curve was obtained for Stiff tia chrysantha on the same nights. 

 Rapid growth was observed as darkness set in, and this al- 

 though no actual shortening of the shoots took place in the 



