V. The Iiiilueuee of Light upou Ihe ürowlh of Leaves. 
131 
course of growth of a leaf of Älliurn Cepa which had bcen thus treated. 
Under ihese circumstances it must be concluded that the growing cells 
of ibe leaves of Allium Cepa are more slowly affecled bj ihe retarding 
action of light than are those of inlernodes and of the leaves of Dicotj- 
ledons, and this may be true also with regard lo Ihe leaves of other 
Monocotyledons. 
It is possible, therefore, to explain all these phenomena of the action 
o ig it upon growth upon the same theory, and this is more salisfaotory 
am more scientific than to attempt to find a dislinct cause for each cne. 
n order to be able to supporl these theorelical considerations b\ 
experimental evidence, 1 made the following experiments with Secale ce- 
1>ea G ’ 3 which Siedler used in many of his observations. 1 sowed 
t ie seeds in small glass boltles filled with moist sand, and, after ger- 
inmation, I placed one of these bottles in a glass jar which was closed 
a cork through which a thermometer passed into the inlerior. Inlo 
this jar a sufficient quantity of concentraled solution of potash was poured 
t° orm a lajer about half an inch thick. The measurernents of Ihe 
giowli ol leaves of the seedlings were made In means of a micro- 
eescope'). The planls were kept in darkness for'al least twelve hours 
»e oie ihe commencement of the observations in order that no persisling 
efiects of the action of light might interfere with the results obtained. 
, leaves were green. 1 found that, when the planls were kept in 
darkness the growth per hour was very nearly uniform, the variations 
>eing such that they might be either altributed to changes of tempera- 
lure or regarded as those irregularities which are always to be detected 
in t e process of growth (»Stossweise Aenderungen« Sachs). In Illustration 
Time. 
llourly 
growth. 
Tempera tu re. 
8 a. rn. 
_ 
9 „ 
0.50 
23.3» C. 
10 » 
0.40 
23.3 
11 „ 
0.40 
23.2 
- 
0.40 
23.0 
I p. in. 
0.30 
23.1 
* » 
0.40 
23.2 
? ” 
0.30 
23.7 
4 „ 
0.50 
23.4 
ü V 
0.30 
22.S 
6 n 
0.40 
22.7 
Hie conuitions were such that no assimilalion 
U , P ° SS1 take P lüCe > an <l yet growth continued. Thal the uniformih 
■c Wi Iure observed is due lo the facl that the planls were not ex- 
10 11 e act ' ou °1 üght. is shewn by variations of this experimenl in 
C lor description of this Instrument see the following paper. 
