542 
foliage leaf, which appears after the coty- 
ledons, caused the first of the bulb scales, 
which normally appear following the foli- 
age leaf, to expand into a foliage leaf. 
In some experiments on the influence of 
light on the form of the leaves Goebel (’96) 
has obtained some interesting results. 
Plants of Campanula rotundifolia were used. 
Tn this species the lower leaves are petioled 
and possess broadly expanded, heart-shaped 
laminz, while the upper leaves are narrow 
and sessile, with intergrading forms. Plants 
in different stages of growth were placed in 
a poorly-lighted room. Young plants which 
had only the round leaves under these con- 
ditions continued to develop only this form 
of leaf, while older plants which had both 
kinds of leaves when the experiment was 
started now developed on the new growth 
of the shoot the round-leaved form. In the 
ease of plants on which the flower shoot 
had already developed, side shoots with the 
round leaves were formed. Excluding the 
possibility of other conditions having an in- 
fluence here, the changes in the form of the 
leaves has been shown to be due to a vary- 
ing intensity of light. The situation of the 
plants in the open favor this view, since the 
leaves near the ground in these places are 
not so well lighted as the leaves higher up 
on the stem. In this case the effect of 
dampness is not taken into account by the 
experimenter, and, since dampness does 
have an influence on the size of the leaf, it 
would seem that it might be at least one of 
the factors here. An attempt was now 
made to prevent the development of the 
round leaves on the young seedlings. For 
this purpose the germinating seeds were 
kept under the influence of strong and con- 
tinuous lighting. The round leaves were 
nevertheless developed in the early stage, 
an indication that this form of the leaf on 
the seedling has become fixed and is hered- 
itary. Hering (’96) found that enclosing 
the larger cotyledon of Streptocarpus in a 
SCIENCE. 
[N.S. Von. VI. No. 145. 
plaster cast, so as to check the growth, the 
smaller and usually fugacious one grew to 
the size of the larger one, provided the ex- 
periment was started before the small one 
was too old. Amputation of the large coty- 
ledon gaye the same results. 
Other experimenters have directed their 
attention to the effect of light and gravity 
on the arrangement of the leaves on the 
stem, as well as the effect of light on the 
length of the petioles and breadth of the 
lamina. Among these may be mentioned 
the work of Weisse (’95), Rosenvinge 
(94), and others. 
Goebel has shown experimentally that 
dampness is also one of the external in- 
fluences which can change the character of 
xerophyllous leaves. A New Zealand spe- 
cies of Veronica of xerophyllous habit and 
scaly appressed leaves in the seedling stage 
has spreading leaves with a broad lamina. 
Older plants can be forced into this condi- 
tion in which the leaves are expanded by 
growing them in a moist vessel (’96). 
Gain, Askenasy and others have shown 
that dampness or dryness has an important 
influence in determining the character of 
the leaves. 
The results of the experiments in showing 
the relation of the leaf to the bud scales 
Goebel regards as evidence that the foliage 
leaf is the original form of the two, and that 
the bud scale is a modification of it. 
Treub (’72) conducted some interesting 
experiments for the purpose of determining 
the homology of the pappus of the Com- 
posite. Gall-insects were employed to 
stimulate the pappus of Hieraciwm wumbel- 
latum, and it was made to grow into a normal 
calyx with five lobes. (A recent letter from 
Professor Treub states that he later re- 
peated these experiments with other species 
of Composite with like results, but the 
work was not published.) Kny (’94) found 
in seedlings and cuttings which he ex- 
perimented with that, while there was still 
