Pinguicula. 5 7 



by my own observations. ITeitlier can there be a doubt 

 that the dissolved nitrogenous constituents of these 

 insects are absorbed by the plants and utilised as nutri- 

 ment ; but no less certain is it that the Pinguiculae (at 

 any rate the four species mentioned above, which I have 

 investigated) flourish perfectly well without animal food, 

 and therefore are not dependent upon it. The primary 

 function of the glandular trichomes on the leaves of 

 Pinguicula, and numerous other plants, is certainly, 

 therefore, to keep off those creeping insects whose 

 bodily dimensions are so small that their visits would 

 not bring about allogamy; but this, of course, does 

 not exclude the possibility of such insects as get 

 caught and remain adherent being digested, and serving 

 as welcome, if not very luxurious, food. 



There are plants in which the glandular trichomes 

 that secrete the viscid matter are set on the higher 

 not on the radical leaves, and are there very abun- 

 dant. If these leaves are so shaped and so placed 



Diatoms in the mucus secreted by the glandular trichomes on the 

 upper side of the leaf, and they appeared quite at home in this 

 medium, lived there for weeks, and apparently, indeed, multiplied. 

 For instance, at InnsbrUok, I scarcely ever failed to find the 

 elegant Epithemia, Argus on Pinguicula alpina. This observation 

 appears to me to throw a ray of light on the significance of the 

 flinty shells of the Diatomaoeae. It is at any rate a very probable 

 supposition that the Diatomacese are protected by these flinty 

 shells against exterior influences which woiild occasion a dis- 

 advantageous chemical change in their protoplasm, as, for example, 

 against the operation of the secretion of the Pinguicula-leaves ; and 

 it appears to me very probable that this secretion may even serve 

 as food for many Diatomacese. 



F 



