ON PROTRUSION OF PROTOPLASMIC FILAMKNTS. 245 



On the Protrusion of Protoplasmic Filaments from the 

 Glandular Hairs on the Leaves of the Common 

 Teasel {Bijisacus syhestris). By Francis Darwin, 

 M.B. (With Plate XIX.) 



The connate leaves of the common teasel [Dipsacus syhestris) 

 form, as is well known, cup-like receptacles surrounding the 

 stem of the plant. In the rain-water accumulating in these cups 

 numerous insects are drowned, and their dead bodies convert the 

 water in which they lie into a strongly animalised fluid. 



In the autumn of 1875 I examined the leaves of the teasel, in 

 the expectation of finding the same evidence of the absorption of 

 the products of decay as may be observed in the remarkable 

 trichomes lining the bladders of Utricularia.^ The glandular 

 hairs or trichomes on the leaves of the teasel proved, however, 

 to be too much shrivelled for the experiment, although the leaves 

 were not themselves withered. In the summer of 1876 I re- 

 commenced the investigation by examining transverse sections of 

 teasel leaves mounted in dilute ammoniacal solutions such as those 

 which are absorbed by the glands of Drosera, Pinguicula, &c., and 

 by the trichomes of Utricularia, and which my father has shown 

 to give rise to the remarkable phenomena of "aggregation.'" 



While examining the transverse section of a teasel leaf (under 

 Hartnack's objective No. 8) I observed a translucent, somewhat 

 highly refracting mass seated on the summit of one of the glands. 

 I imagined it to be resin, excreted in the form of a fila- 

 mentous mass. I was therefore astonished to observe a few 

 moments later that its shape had distinctly altered. On finding 

 similar filaments on several neighbouring glands I became con- 

 vinced that the subject was well worth investigation. 



The first idea that presented itself was that the filaments were 

 protoplasmic organs specially adapted for the absorption of the 

 fluid containing decayed animal matter collected in the teasel 

 cups. This theory was overthrown by the following facts. The 

 teasel is a biennial, and during its first year's growth consists of 

 a mere rosette of radical leaves, the cup-bearing stem being 

 formed during the second year. But the supposed pseudopodia 

 are found not only on the connate leaves of the second year's 

 growth but on the radical ones produced during the first season. 

 Tliey are also found in Bipsacus pilosus, whose leaves are not 

 sufficiently connate to retain water, and which can therefore 

 capture no insects. These facts prove conclusively that, whether 



* * Insectivorous Plants,' p. 418. 



vol. XVIT. NEW SER. R 



