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Show 140 DROSERA ROTUNDIFOLIA. C HAP. VII. amount of inflection is utterly insignificant, as we shall hereafter see, compared with that caused by very weak solutions of several salts of ammonia. · Plants which have lived for some time in a rathet· high temperature are far more sensitive to the action of water than those grown out of doors, or recently brought into a warm greenhouse. Thus in the above seventeen cases, in which the immersed leaves had a considerable number of tentacles inflected, the plants had been kept during the winter in a very warm greenhouse; and they bore in the early spring remarkably fine leaves, of a light red colour. Had I then known that the sensitiveness of plants · was thus increased, perhaps I should not have ~sed the leaves for my exp~riments with the very weak solutwns of phosphate of ammonia; but my experiments are not thus vitiated, as I invariably used leaves from the same plants for simultaneous immersion in water. It often happened that some leaves on the same plant, and some tentacles on the same leaf, were more sensitive than others; but why this should be so, I do not know. Besides the differences just indicated between the leaves imFIG. 9. (Drosera rotundifolia.) LeaF (enlarged) with all the tentacles close ly inflected, from immersion in a solution of phosphate of ammonia (one part to 87,500 of water). mersed in water and in weak solutions of ammonia, the tentacles of the latter are in most cases much more closely inflected. The appearance of a leaf after immersion in a few drops of a solution of one grain of phosphate of ammonia to 200 oz. of water (i.e. one part to 87,500) is here reproduced: such energetic inflection is never caused by water alone. With leaves in the weak solutions, the blade or lamina often becomes inflected ; and this is so rare a circumstance with leaves in water that I have seen only two instances ; and in both of these the inflection was very feeble. Again, with leaves in the weak solutions, the inflection of the ten-tacles and blade often goes on steadily, though slowly, increasing during many hours ; and CHAP. VII. 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 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' nothing could be more variable. In both cases the exterio~ 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. w~ole day, or even two d~ys ; .but as a general rule they remain Inflected for a longer periOd In very weak solutions than in water. In solut~on~ 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 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 water and in the solutions will be described, the reader can judge for himself. CARBONATE 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 |