CHAP. XV, THEIR POWER OF ABSORPTION. 353 



has shown * that tobacco plants supplied with the vapour of 

 carbonate of ammonia yield on analysis a greater amount of 

 nitrogen than other plants not thus treated; and, from what 

 we have seen, it is probable that some of the vapour may be 

 absorbed by the glandular hairs. 



Summary of the Observations on Glandular Hairs. 

 From the foregoing observations, few as they are, we 

 see that the glands of two species of Saxifraga, of a 

 Primula and Pelargonium, have the power of rapid 

 absorption ; whereas the glands of an Erica, Mirabilis, 

 and Nicotiana, either have no such power, or the 

 contents of the cells are not affected by the fluids 

 employed, namely a solution of carbonate of am- 

 monia and an infusion of raw meat. As the glands 

 of the Mirabilis contain protoplasm, which did not 

 become aggregated from exposure to the fluids just 

 named, though the contents of the cells in the blade 

 of the leaf were greatly affected by carbonate of 

 ammonia, we may infer that they cannot absorb. We 

 may further infer that the innumerable insects caught 

 by this plant are of no more service to it than are 

 those which adhere to the deciduous and sticky scales 

 of the leaf-buds of the horse-chestnut. 



The most interesting case for us is that of the two 

 species of Saxifraga, as this genus is distantly allied 

 to Drosera. Their glands absorb matter from an 

 infusion of raw meat, from solutions of the nitrate 

 and carbonate of ammonia, and apparently from 

 decayed insects. This was shown by the changed 

 dull purple colour of the protoplasm within the cells 

 of the glands, by its state of aggregation, and appa- 

 rently by its more rapid spontaneous movements. 



* ' Comptes rendus,' June 15, 1871. A good abstract of this paper 

 K given in the 'Gardener's Chronicle,' July 11, 1874. 



