VI. Tlie Iufluence of Light «pon the Growth of unicellular Organs. 137 
analysis of the variations ma\ be made in the following inanner. If the 
diiference betvveen the observed maximuni and minimum be divided by 
the number of hours intervening between the times of their occurrence, 
an average acceleralion is oblained, which may be regarded as the acce¬ 
leration due to the course of the grand period. The difference between 
the average acceleration per hour and the observed acceleration will be 
the acceleralion due lo variations in the external condilions. The average 
acceleration in this case is ^ ^ ^ = 0-26 nearly. After the 
maximum has been attained, growth may be regarded as not uudergo- 
ing, for a time, any alteration beyond that produccd by varying external 
condilions. 
2.30 
2.90 
_2.90 
_ 
2 30 — 0.26 
_ 
0.34 
3.10 
... 3.10 
— 
2.90 — 0.26 
= 
0.06 — 
3.20 
_3.20 
— 
3.10 — 0.20 
= 
0.16 — 
3.50 
_3.50 
— 
3.20 — 0.26 
= 
0.04 + 
3.60 
-3.60 
— 
3.50 - 0.26 
= 
0.16 — 
3.70 
_3.70 
— 
3.60 — 0.26 
= 
0.16 — 
4.10 
_4.10 
— 
3.70 — 0.26 
= 
0.14 + 
3.90 
_3.90 
— 
4.10 
== 
0.20 — 
3.70 
_3.70 
— 
4.10 
= 
0.40 — 
3.80 
_3.80 
— 
4.10 
SS 
0.30 — 
4.00 
_4.00 
— 
4.10 
= 
0 10 — 
The signs after the figures in the last column shevv wliether the observed 
acceleration has been greater or less than the average acceleration. When 
the plus sign is used, il has been greater, when the minus sign, it has 
been less. 
lt appears tberefore, that the curve of the grand period undergoes 
considerable variations under tolerably constant condilions. The effects 
of varying condilions may now be sludied. 
The following table with ils accompanying curve shews how the 
course of the grand period is affected, when the plant is exposed to aller- 
nations of light and darkness. 
am 
1 
llouily 
growth. 
Tempera- 
ture. 
8—9 
a. ui. 
2.70 
22.90C. 
10 
j; 
2.70 
24.3 
11 
» 
2.30 
26.0 * 
12 
— 
2 90 
25.0 
1 
p. in. 
2.70 
25.8* 
2 
r? 
3.20 
25.3 
3 
,, 
3.50 
25-2 
4 
ti 
2.90 
25.0* 
5 
» 
3.20 
25.1 
6 
2.80 
25.3 
* exposed lo light. 
