42 
THE JOURNAL OF ROTANY 
phenomenon by hazarding the surmise that the plant exudes into 
the water, when accumulated, some strong-smelling or sweet-tasting 
toxic substance which first attracts insects and other small creatures 
and then narcotizes or intoxicates them, leading them to fall in and 
get drowned. Their subsequent putrefaction is, doubtless, due (in the 
main, at any rate) to bacterial infection from the air. 
That insects really are both attracted and stupefied in some way 
by the liquor seems proved by an observation I made on 25 August 
1916. Early in the morning of that day, I happened to notice a 
newly-dead individual of the Large White Butterfly {Pieris brassices') 
floating in the putrescent liquor in one of the upper cups of one of a 
group of plants of the cultivated Teasel # growing in my garden. 
Whilst I was fishing out and examining the insect, I was surprised 
to see two other W r hite Butterflies, till then unnoticed, fly up from 
one of the lower cups, having been disturbed, no doubt, by the slight 
shaking I had given the whole plant. That these two butterflies had 
become, in some way, more or less stupefied through imbibing the 
liquor seems to me certain; for they did not fly up till some time 
(perhaps a quarter of a minute) after I had begun my examination ; 
whereas, had they been normally alert, they would have taken flight 
immediately I began my examination of the plant, or even before 
I had approached it closely, being, like all butterflies, very shy by 
nature. 
Further evidence to the same effect seems to be provided by the 
fact, already cited, that I have found slugs (generally, I believe, 
Limax agrestis) and several species of snail (including Helix 
cantiana) dead in the cups ; while Sir Francis Darwin found “ large 
slugs ” in them. Now all these molluscs (which find no difficulty in 
crawling up a perpendicular glass window-pane) could surely, in 
ordinary circumstances, have crawled with ease up the sides of the 
Teasel-cups, in spite of their exceedingly steep and smooth sides. 
Indeed, Sir Francis says : “ I find that slugs, if dropped into the 
teasel-cups, can crawl up the smooth leaves [i. e ., the sides of the 
cups].” The obvious conclusion is, therefore, that those molluscs 
which failed to crawl out, had been stupefied or intoxicated in some 
way and drowned through imbibing the liquor. 
The presence in the fluid of some such intoxicating element was 
suspected, many years ago, by Sir Francis, who says:—“ I tried a 
number of experiments by taking a large number of . . . malacoderm 
beetles and placing one half in water, the other in the fluid of the 
Teasel-cups. The result showed that beetles are drowned much more 
readily in the Teasel fluid than in pure water. Whether there is 
a narcotising poison in the fluid or whether, as is far more probable, 
the oiliness or stickiness of the decaving fluid causes the insects’ 
spiracles to be blocked up, I cannot say.” 
In this connexion, it may be noted again that most of the small 
creatures commonly found in the cups are notoriously addicted to foul 
feeding—the Diptera and some Coleoptera, in particular. Even the 
* This, though generally spoken of as a distinct species (P. fullonum, the 
“ Fuller’s Teasel ”), is probably no more than a variety of P. sylvestris , slightly 
altered by long cultivation. 
