172 FRANCIS DARWIN. 



It has been shown that the filaments are protoplasmic 

 bodies, containing a large quantity of resinous matter. The 

 question next arises, with what processes in plant-physiology 

 is the protrusion of filaments homologous? ; 



The leaf-glands of the teasel are similar in general struc- 

 ture to many glandular hairs which produce resinous and 

 slimy secretions ; and, like these glands, they contain bright 

 drops of secreted resin, lying in the centres of the gland- 

 cells ; they also resemble many glandular hairs, in being 

 often capped with accumulations of secreted matter. Now, 

 these accumulations stain red with alkanet, yellow with 

 iodine, and are largely soluble in alcohol — that is to say, 

 they consist of substances which have the same reactions as 

 the filaments. There is, in fact, no doubt that the caps of 

 resinous matter on the teasel-glands are produced by the 

 accumulation of dead filaments. According to this view, the 

 act of protrusion is essentially a process of secretion ; the 

 resin issues from the gland-cells, mingled with a certain 

 amount of true protoplasm ; and it is only from the death 

 of the living or protoplasmic part of the filaments that the 

 resinous accumulation results. This view of the act of pro- 

 trusion corresponds with the theory of secretion held by some 

 physiologists, viz. that secreted matter is produced by the 

 dissolution or death of protoplasm. That, for instance, the 

 oil in a fat-cell is the result of the disintegration of a plastid 

 or individualised mass of protoplasm, formed in the cell by 

 endogenous cell-formation. 



The protrusion of protoplasmic filaments from the glands 

 of the teasel appears to bear an obscure relationship to the 

 phenomena of " aggregation " in Drosera and several other 

 plants. In both processes we have homogeneous, highly 

 refracting protoplasmic masses, which undergo amoeboid 

 movements, and are in some unknown way connected with the 

 absorption of nitrogenous matter. In Drosera the proto- 

 plasmic masses remain within certain cells, in Dipsacus they 

 are protruded through the cell-wall. 



When we begin to inquire as to the function of the fila- 

 ments, the answer seems at first to be sufficiently plain, but 

 this is very far from being the case. The connate leaves of 

 the teasel form cup-like cavities, which become full of rain 

 and dew, and in which many drowned insects accumulate. 

 The glands on the lower portions of the leaves are thus 

 exposed to a highly nitrogenous fluid. And since such 

 fluids are known to produce a remarkable effect on the fila- 

 ments exposed to them, it seems probable that the filaments 

 are in some way connected with the assimilation of food 



