334 Robinson . — Experiments on the Effect of External Stimuli 
leaf fragments of Pelargonium , Primula vulgaris , and Eucalyptus globulus. 
None of the sporidia germinated normally in the vicinity of fragments of 
the leaves of Pelargonium and Primula vulgaris . The sporidia in these 
cultures, however, made many abortive attempts at germination. Instead 
of putting out a normal germ tube the sporidium became distended, giving 
rise to one or more bud-like structures (Fig. 2). The contents of these 
were granular and contrasted strongly with the hyaline appearance of 
the normal germ tubes. These abortive germ tubes did not grow any 
further. 
Similar abnormal germinations were observed where fragments of the 
leaves of Eucalyptus globulus were used, but here the inhibitory effect on 
germination was not so strongly marked ; for some of the sporidia in each 
culture germinated normally. In one of these experiments with Eucalyptus 
a series of counts was made of the actual numbers of sporidia which, 
respectively, germinated normally, abnormally, or not at all. These counts 
were taken in successive areas, moving from the leaf fragments outwards to 
the margin of the drop. Table I shows the results of these counts. 
Table I. (Exp. 35, Series II.) 
Area next 
Total No. 
of spores in 
area. 
No. of spores 
showing 
normal ger- 
mination. 
No. of spores 
shozuing 
abortive ger- 
?nination. 
No. of 
spores 
not ger- 
minated. 
% of nor- 
mal ger- 
mination. 
% of ab- 
normal ger- 
mination. 
leaf fragment 
1 
. . 66 . 
• • 13 • • 
. 44 . . 
. 9 . 
. 19 . 
. 66 
2 
. . 80 . 
. . 17 . . 
• 35 • ■ 
. 28 . 
. 21 
• 43 
3 
• • 57 • 
. . 16 . . 
. 9 . . 
• 32 • 
. 28 . 
• 15 
4 
• • 55 • 
. . 11 . . 
• 5 • • 
• 39 • 
. 20 
9 
5 
. . 46 . 
• • *3 • • 
1 . . 
. 32 . 
. 26 
. 2 
6 
. . 68 . 
. . 62 . . 
. — . . 
. 6 . 
. 91 . 
— 
Area most 
remote 
from 
leaf fragment 
7 
• • 55 • 
• • 55 • • 
. — . 
. 100 
. — 
The two columns on the extreme right give percentages obtained from 
the figures in the corresponding counts. The percentage of sporidia which 
germinated at all, near the fragment, was small, but increased on moving 
away, until on the margin of the drop 100 per cent, of the sporidia 
germinated normally. More striking, however, is the fact that the per- 
centage of abnormal germinations was greatest near to the leaf fragment, 
and gradually diminished to nil on the margin of the drop. 
It seemed possible that in the experiments with the fragments of 
garden geranium leaf, the substance which affected the germination of the 
sporidia might be localized in the glandular hairs of the leaf. An experi- 
ment was accordingly set up, in which the sporidia were allowed to 
germinate near to a fragment from which the epidermis had, been carefully 
removed. In this case excellent germination took place. It has been 
mentioned above that where a fragment of the leaf of Geranium Robertianum 
