TTTE COMMON TEASEL AS A CAENTYOEOUS PLANT 
37 
trouais successivement toutes les feuilles n’en a pas para souffrir clans sa 
vegetation.” 
On the whole, it seems probable that the Teasel does derive some 
direct benefit from the water it catches in its cups. At the same 
time, it may be recognized that the plant is one not likely to be often 
in serious need of such succour; for it grows as a rule in fairly damp 
situations, not particularly likely to be affected by drought. Without 
doubt, therefore, the plant’s habit of collecting and storing water in 
its cups is also of use to it in some other and more specialised way 
or ways. 
One such use of the water-cups has been suggested by many 
writers : namely, that of protecting the nectar or pollen of the plant 
against wingless robber-insects, which, were the water absent, might 
crawl up the stem and steal either or both. In much the same way, 
the nectar of Lychnis, Silene, Hyoscyamus , and many other “catch- 
fly” plants is protected by a sticky exudation on the stem or leaves, 
which catches and holds small crawling insects. As long ago as 
1789, Erasmus Darwin asserted (/. c) that the water-cups of the 
Teasel served “ to prevent insects from creeping up to devour its 
seed [meaning pollen].” Since his time, many other botanists have 
accepted the same idea :—see, for example, Kircbner ( Flora von 
Stuttgart, pp. 678-679 : 1888), Francis Darwin (op. cit.'), Lubbock 
(Ants, Bees, and Wasps, 8th ed., p. 52 : 1886), and Ainsworth- 
Davis (The Flowering Blant, p. 112: 1890). 
That the water-cups of the Teasel are capable of serving this 
purpose effectively is certain. Yet, for several reasons, one may 
doubt whether, in fact, they really do so serve to more than a very 
small extent, if at all. 
In the first place, the stem of the plant is so tall, so smooth, and 
so well provided with thorn-like downward-pointing prickles, that the 
number of insects capable of crawling up it and reaching the flowers, 
six or seven feet above the ground, must be infinitesimally small. 
In the second place, of the very few small creeping insects capable of 
achieving this feat, few or none would be able to benefit by it; for 
the flowers of the Teasel (which are adapted for pollination, and are 
visited freely by long-tongued lepidopterous and liymenopterous 
insects—see Muller, Fertilization of Flowers, 308, and Knuth, 
Pollination, ii. 557) have corolla-tubes from 10 to 13 mm. in length, 
about 2 mm. in width at the entrance, and taper at the bottom to so 
narrow a point that no insect, however small, likely^ to be capable 
of crawling up the stem and reaching the flowers could enter, and 
none but flying insects having a tongue almost or quite 10 mm. in 
length could possibly reach the nectar. 
It seems clear, therefore, that the primary object of the collection 
of water in the cups is neither the succour of the plant in time of 
drought nor the protection of its nectar against predatory insects. 
It appears more probable, from facts to be given hereafter, that the 
main object of the plant in collecting water is the catching and 
drowning therein of the many small creatures already mentioned, 
and that their juices, after putrefaction, are digested (or, at any rate, 
absorbed) by the plant. Other members of the genus Dipsacus, but 
not all, also possess this insect-catching habit. 
