270 ruAxcis darwinj. 



many smaller flies and much debris, A much lar^'er number of 

 insects were counted in some other teasel-cups, but the notes 

 were lost, and the loss was only discovered when it was too late 

 to make fresh observations. The water contained in the cups is 

 almost always muddy Irom the debris of dead insects ; and when 

 the old leaves at the base of the stem wither, and can no longer 

 liold water I have seen them swarming with Staphylinidse and 

 other refuse-eating beetles. T tried a number of experiments by 

 taking a large number of the same kind 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 

 rapidly in the teasel fluid than in pure water. Whether there is 

 a narcotizing poison in the fluid, or whether, as is far more pro- 

 bable, the oiliness or stickiness of the decaying fluid causes the 

 insect's spiracles to be blocked up, I cannot say. The fact that 

 large slugs are occasionally drowned in the cups is in favour of 

 the poison hypothesis, for I find that slugs, if dropped into the 

 teasel-cups, can crawl up the smooth leaves. 



From these various considerations I believe that the plant 

 does profit by the insects caught in the cups. This question 

 I hope to decide by a comparative experiment, in which a number 

 of teasels raised from seed under similar conditions will be 

 divided into two lots, one half being starved and the other fed 

 with insects or pieces of meat. 



But whether or not the glands which find themselves immersed 

 in the putrid fluid of the teasel-cups take advantage of their 

 position to absorb nitrogenous matter, there is no doubt that the 

 protrusion of filaments is not a habit originally developed for 

 this special purpose ; for, as above explained, the glands on the 

 seedlings which do not form cups, and therefore catch no insects, 

 have well-developed filaments. But it may be answered that 

 they are developed in the seedlings by a kind of inheritance from 

 the adult plant. Even if this reasoning were permissible the con- 

 clusion that the filaments are specially ada|)ted in relation to the 

 leaf-cups is demolished by the following fact, already alluded to. 

 The other British species of teasel, I), pilosus, has no leaf-cups, 

 and therefore cannot entrap insects, yet the leaves bear glands, 

 and these produce contractile filanients. If we grant that the 

 filaments have any power of absorbing nitrogenous fluids, and 

 this can hardly be denied, the only theory that suggests itself is 

 the following : — That the filaments absorb the salts of ammonia 

 from the rain-water and dew which fall on the leaves, and that it 

 is this power which is modified in the adult plant so as to enable 

 the filaments to take advantage of the animalized fluid retained 

 by the leaf-cups. It has been already stated that filaments can 

 issue from the glands when the leaf is merely damp. It does 



