CHAP. VIL CARBONATE OF AMMONIA. 141 



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 some- 

 times 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, 

 nothing could be more variable. In both cases the exterior 

 tentacles not rarely begin 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 

 difficult to distinguish between the effects of water and the 

 weaker solutions ; but in truth there is not the slightest diffi- 

 culty 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 water and in the solutions will be described, 

 the reader can judge for himself. 



CARBONATE OF AMMONIA. 



This salt, when absorbed by the roots, docs 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 ob- 

 served. 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 ab- 

 sorbent hairs were not visibly affected. The tentacles 



