884 VEGETABLE GEOWTfi. 



wheel, leaves its trace as it ascends or descends. The wheel is 

 caused to move by means of a second balanced thread which 

 passes over its axis, and which is fastened at one end to the 

 growing part of the plant. 



1006. Pfeffer's modification of this apparatus provides that the 

 cylinder shall turn a short distance at regular intervals of time, 

 so that the line made by the needle becomes interrupted and thus 

 exhibits the appearance of steps ; in which the height of the step 

 represents the total ascent or descent of the needle during a 

 given time, while the other line of the step merely marks the dis- 

 tance through which the cylinder moves at the close of one of its 

 intervals. 



1007. Examples of very rapid growth are afforded by many 

 fungi ; for instance the common puff-ball, which increases enor- 

 mously in size during a single night. 



Shoots of bamboo have been observed at Kew to grow at the 

 rate of two to three inches in the twenty-four hours ; and in its 

 native habitat, Bambusa gigantea has been known to grow more 

 than ten inches a day. 



The expansion of the leaves of Victoria regia is extremely 

 rapid, under favorable conditions reaching a foot in the twenty- 

 four hours. The scapes of many plants develop at a rapid rate, 

 and afford excellent material for practice with the auxanometer. 



1008. Conditions of growth. Vegetable growth does not take 

 place unless there is an available supply of assimilated matter, 

 access of free oxygen, and a sufficiently high temperature. The 

 assimilated matter may be furnished to the growing parts di- 

 rectly from green tissues, or from reservoirs where it has been 

 stored up. In either case it must come in a state of solution to 

 the growing cells, and hence a certain amount of water is re- 

 quired for the transfer. That the amount of water demanded is 

 not necessarily large, is shown by the starting of shoots from 

 bulbs, tubers, etc., in the spring, even when no water has been 

 furnished from outside. 



1009. Although the process of respiration in green plants may 

 go on for a time without free oxygen, as has been shown by the 

 experiments described on page 371, there is no proof that growth 

 occurs under such circumstances. In an atmosphere of hydrogen, 

 nitrogen, carbonic acid, or nitrous oxide, gases which are not 

 in themselves harmful to plants, growth does not take place, 

 as has been proved by experiments upon seeds and seedlings. 

 Detmer has shown that growth is immediately checked when the 

 plant is deprived of free oxygen, but death does not ensue until 



