. XV. THEIK TOWER OF ABSORPTION. 345 



tho species of Droseracege absorb various fluids or 

 at least allow them readily to enter,* it seemed desir- 

 able to ascertain how far the glands of other plants 

 which are not specially adapted for capturing insects, 

 had the same power. Plants were chosen for trial 

 at hazard, with the exception of two species of saxi- 

 frage, which were selected from belonging to a family 

 allied to the Droseracea3. Most of the experiments 

 were made by immersing the glands either in an in- 

 fusion of raw meat or more commonly in a solution of 

 carbonate of ammonia, as this latter substance acts so 

 powerfully and rapidly on protoplasm. It seemed also 

 particularly desirable to ascertain whether ammonia 

 was absorbed, as a small amount is contained in rain- 

 water. With the Droseraceae the secretion of a viscid 

 fluid by the glands does not prevent their absorbing ; so 

 that the glands of other plants might excrete super- 

 fluous matter, or secrete an odoriferous fluid as a 

 protection against the attacks of insects, or for any other 

 purpose, and yet have the power of absorbing. I 

 regret that in the following cases I did not try whether 

 the secretion could digest or render soluble animal 

 substances, but such experiments would have been 

 difficult on account of the small size of the glands 

 and the small amount of secretion. We shall see in 

 the next chapter that the secretion from the glandular 

 hairs of Pinguicula certainly dissolves animal matter. 



S ixifraga umbrosa. The flower-peduncles and petioles of the 

 leaves are clothed with short hairs, bearing pink-coloured glands, 

 formed of several polygonal cells, with their pedicels divided by 

 partitions into distinct cells, which are generally colourless, but 

 Bometimes pink. The glands secrete a yellowish viscid fluid, by 



* The distinction between true clearly understood : see Miiller's 

 Absorption and mere permeation, ' Physiology,' Eng. translat. 1838 

 or imbibition, is by no means vol. i. p. 280. 



