Chap. VII J CARBONATE OP AMMONIA. 115 



caused by water alone. With leaves in the weak solutions, the 

 blade or lamina often becomes inflected; and this is so rare a cir- 

 cumstance with leaves in water that I have seen only two in- 

 stances; and in both of these the inflection was very feeble. Again, 

 with leaves in the weak solutions, the inflection of the tentacles 

 and blade often goes on steadily, though slowly, increasing during 

 many hours; and this again is so rare a circumstance with leaves 

 in water that I have seen only three instances of any such increase 

 after the first 8 to 12 hrs.; and in these three instances the two 

 outer rows of tentacles were not at all affected. Hence there is 

 sometimes a much greater difference between the leaves in water 

 and in the weak solutions, after from 8 hrs. to 24 hrs., than there 

 was within the first 3 hrs.; though as a general rule it is best to 

 trust to the difference observed within the shorter time. 



With respect to the period of the re-expansion of the leaves, 

 when left immersed either in water or in the weak solutions, noth- 

 ing could be more variable. In both cases the exterior tentacles 

 not rarely b^n to re-expand, after an interval of only from 6 to 

 8 hrs.; that is just about the time when the short tentacles round 

 the borders of the disc become inflected. On the other hand the 

 tentacles sometimes remain inflected for a whole day or even two 

 days ; but as a general rule they remain inflected for a longer 

 period in very weak solutions than in water. In solutions which 

 are not extremely weak, they never re-expand within nearly so 

 short a period as six or eight hours. From these statements it 

 might be thought diflScult to distinguish between the effects of 

 water and the weaker solutions; but in truth there is not the 

 slightest difficulty until excessively weak solutions are tried; and 

 then the distinction, as might be expected, becomes very doubtful, 

 and at last disappears. But as in all, except the simplest, cases, 

 the state of the leaves simultaneously immersed for an equal 

 length of time in M-ater and in the solutions will be described, the 

 reader can judge for himself. 



C^BONATE OF AMMONIA. 



This salt, when absorbed by the roots, does not cause the 

 tentacles to be inflected. A plant was so placed in a solution 

 of one part of the carbonate to 146 of water that the young 

 uninjured roots could be observed. The terminal cells, which 

 were of a pink colour, instantly became colourless, and their 

 limpid contents cloudy, like a mezzo-tinto engraving, so that 

 some degree of aggregation was almost instantly caused; 

 but no further change ensued, and the absorbent hairs were 

 not visibly affected. The tentacles did not bend. Two other 

 plants were placed with their roots surrounded by damp moss, 

 in half an ounce (14.198 c.c.) of a solution of one part 

 of the carbonate to 218 of water, and were observed for 

 9 



