GLANDULAR HAIRS OF THE COMMON TEASEL. 173 



material. It seems probable that, either with or without the 

 assistance of their filaments, the glands do absorb some 

 nitrogenous matter; for movements of their cell-contents 

 occasionally occur, which can only thus be interpreted. 

 But on account of the rarity and uncertainty of these aggre- 

 gation changes within the glands, but little weight must be 

 allowed to the phenomena as a proof of the absorbing capacity 

 of the glands. 



Some other points, however, in the structure of the plant 

 render it almost certain that the connate leaves are specially 

 adapted to serve some useful purpose. Kerner is probably 

 right in believing that the " cups " of the teasel are of use 

 to the plant in keeping off nectar-stealing ants and other 

 wingless insects. But unless this is their only function, it 

 seems probable that the connate leaves have been, to a 

 certain extent, adapted for the capture of insects whose 

 decaying remains are absorbed by the plant. The leaves are 

 smooth and steeply inclined, and form a pair of treacherous 

 slides leading down to a pool of water. 



It is worthy of note that the leaves of the first year's 

 growth, which do not form cups, are not smooth, but bristle, 

 with long sharp hairs ; moreover in Dipsacus pilosus the 

 leaves (of the second year's growth) are not sufficient connate 

 to form cups, and they also are rough with hairs. These 

 facts seem to show that the smoothness of the second-year 

 leaves in D. sylvestris is a specially acquired quality. 

 Another special point of structure in D. sylvestris may be 

 noted — the prickles on the stem end abruptly above the level 

 of the water in the " cups," and thus avoid supplying a 

 ladder of escape to the drowning victims. Even if we grant 

 from the above considerations that the filaments protruded 

 from the glands are in some way connected with the absorp- 

 tion of nitrogenous matter from the putrid fluid in the cups, 

 we are far from understanding the whole of the problem. 

 For precisely similar^/amew^-;pro^rM(/m^ glands are found on 

 the seedling leaves of D. sylvestris, and on the second year's 

 leaves of D. pilosus ; and as no " cups " are formed in either 

 of these cases, the filaments cannot be connected with ab- 

 sorption of the products of decay. The only view which 

 suggests itself is that the filaments absorb ammonia from the 

 dew and rain. Recent researches have shown that certain 

 leaves have the power of absorbing an appreciable quanlity 

 of ammonia, and this fact lends some probability to the view 

 above advanced. 



To recapitulate : — Protoplasmic filaments are protruded 

 from the leaf-glands on the teasel; and the only theory 



