Chap. XL] GENERAL SUMMARY. 219 



enamel of teeth, but this is simply due to the large quantity 

 of acid secreted, owing, apparently, to the desire of the plant 

 for phosphorus. In the case of bone, the ferment does not 

 come into play until all the phosphate of lime has been de- 

 composed and free acid is present, and then the fibrous basis 

 is quickly dissolved. Lastly, the secretion attacks and dis- 

 solves matter out of living seeds, which it sometimes kills, 

 or injures, as shown by the diseased state of the seedlings. 

 It also absorbs matter from pollen, and from fragments of 

 leaves. 



The seventh chapter was devoted to the action of the 

 salts of ammonia. These all cause the tentacles, and often 

 the blade of the leaf, to be inflected, and the protoplasm to 

 be aggregated. They act with very different power; the 

 citrate being the least powerful, and the phosphate, owing, 

 no doubt, to the presence of phosphorus and nitrogen, by far 

 the most powerful. But the relative efiiciency of only three 

 salts of ammonia was carefully determined, namely the car- 

 bonate, nitrate, and phosphate. The experiments were made 

 by placing half-minims (.0296 c.c.) of the solutions of differ- 

 ent strengths on the discs of the leaves, by applying a min- 

 ute drop (about the yV of a minim, or .00296 c.c.) for a few 

 seconds to three or four glands, and by the immersion of 

 whole leaves in a measured quantity. In relation to these 

 exx)eriments it was necessary first to ascertain the effects of 

 distilled water, and it was found, as described in detail, 

 that the more sensitive leaves are affected by it, but only in 

 a slight d^ree. 



A solution of the carbonate is absorbed by the roots and 

 induces aggregation in their cells, but does not affect the 

 leaves. The vapour is absorbed by the glands, and causes 

 inflection as well as aggregation. A drop of a solution con- 

 taining tiv of a grain (.0675 mg.) is the least quantity 

 which, when placed on the glands of the disc, excites the 

 exterior tentacles to bend inwards. But a minute drop, con- 

 taining irirnr of a grain (.00445 mg.), if applied for a few 

 seconds to the secretion surrounding a gland, causes the 

 inflection of the same tentacle. When a highly sensitive 

 leaf is immersed in a solution, and there is ample time for 

 absorption, the yrsSniir of a grain (.00024 mg.) is sufficient 

 to excite a single tentacle into movement. 



