110 



Upon the rate of growth by Plants 



probable that something of this kind takes place in nature : a period 

 of vigorous developement, requiring a great expenditure of vital 

 energy, being followed by comparative torpor till the vital powers 

 are recruited. For example the successive growths of the Willow 

 are represented by the numbers 10, 26, 20, 20, 25, 26, 26, 10, 42, 

 31, 45, 17, 19, 40, 18 ; of the Fig, whose general slow progress is 

 unfavourable to this kind of observation, by 12, 22, 21, 03, 11, 11, 

 16, 15, and 11, 14, 11, 03, 22, 13, 13, 04 ; of the Passionflower by 

 20, 11, 60, 05, 14, 03, 20, 47, 17, 17, 22 and 26, 16, 76, 33, 40, 50, 

 29, 29, 34, 24, 50, 35 ; and of the Vine by 20, 34, 12, 32, 55, 31, 

 31, 37, 62, 54, 28, 52, 74, 50, 14, 22, 38; and so on. Although 

 this kind of oscillation is not absolutely constant, yet it is so very 

 usual, as to appear to be a part of the customary habit of vegeta- 

 tion ; and is yet more striking if we turn to the instances of most 

 rapid growth in the four cases before us ; for they are invariably 

 succeeded by a corresponding decrease of growth. For example 

 the willow occasionally lengthened as much as four tenths or even 

 more than five tenths of an inch in six hours ; these were invariably 

 succeeded by a considerable reduction in growth ; thus .42 sunk to 

 .31, .45 to .17, .40 to .18, .40 to .17, and .43 to .20. The maxi- 

 mum of developement in the Fig was rather more than two tenths 

 of an inch in 6 hours ; when this or any similar rate was observed the 

 numbers stood thus ; .22 fell to .13, .19 to .15, .20 to .10. In the Pas- 

 sionflower the greatest growth was rather more than eight tenths of 

 an inch in six hours ; here .82 fell to .10, .79 to. 34, .70 to .27. And 

 finally the Vine, which on one occasion grew nearly nine tenths of 

 an inch in six hours, is found to obey the same apparent law ; for 

 .89 is followed by .63, .70 by .47, .74 by .50, .71 by .30, and so on. 



Another subject of consideration is the cause or causes that tend 

 to produce the fastest and the slowest growth. Fluctuations of 

 temperature can hardly have had any connection with this, because 

 the plants were grown, as has been stated, in a hothouse, the heat 

 of which was maintained at about 73° by day and 65° by night. 



