208 



NATURE 



{July 15, 1875 



protoplasmic contents of the cells of the gland and of 

 those lying immediately beneath it ; though the two 

 phenomena are not necessarily connected with one 

 another. If the tentacles of a young but mature leaf that 

 has never been excited or become inflected, are examined, 

 the cells forming the pedicels are seen to be filled with a 

 homogeneous purple fluid, the walls being lined with a 

 layer of colourless circulating protoplasm. If a tentacle is 

 examined some hours after the gland has been excited by 

 repeated touches, or by an inorganic or organic particle 

 placed on it, or by the absorption of certain fluids, the 

 purple matter is found to be aggregated into masses of 

 various shapes suspended in a nearly or quite colourless 

 fluid. This change commences within the glands, and 

 travels gradually down the tentacles ; and the aggregated 

 masses of coloured protoplasm are perpetually changing 



Fig. z.— {Drosera roinndt/olia.) 

 Leaf (enlarged) with all the ten- 

 tacles closely inflected, from im- 

 mersion in a solation of phosphate 

 of ammonia (one part to 87,500 of 

 water). 



Fig. 2. — {Drosera rotundi/olia.) 

 Leaf (enlarged) with the tentacles 

 on one side inflected over a bit of 

 meat placed on the disc. 



their form, separating, and again uniting. Shortly after 

 the tentacles have re-expanded in consequence of the 

 removal of the exciting substance, these little coloured 

 masses of protoplasm are all re-dissolved, and the purple 

 fluid within the cells becomes as homogeneous and trans- 

 parent as it was at first. This process of aggregation is 

 independent of the inflection of the tentacles and of 

 increased secretion from the glands ; it commences 

 within the glands, and is transmitted from cell to cell 

 down the whole length of the tentacles, being arrested for 

 a short time at each transverse cell-wall. The most 

 remarkable part of the phenomenon is that even in those 

 tentacles which are inflected, not by the direct irritation 

 of their glands, but by an irritation conducted from other 

 glands on the leaf, this aggregation of the protoplasm 

 still commences in the cells of the gland itself. 



Some who admit the reality of the phenomena now 

 described, have still doubted the digestive power ascribed 

 to the leaves of the Sundew, believing that the apparent 

 absorption of the organic substances in contact with the 

 glands is due rather to their natural decay. This question 

 is, however, entirely set at rest by Mr. Darwin's observa- 

 tions. The action of the secretion from the glands on all 



albuminous substances — for it is by these only among 

 fluids that inflection of the tentacles is excited— is pre- 

 cisely the same as that of the gastric juice of animals. 

 The secretion of the unexcited glands is neutral to test- 

 papers ; after irritation for a sufficiently long period it is 

 distinctly acid. A very careful analysis by Prof. Frank- 

 land of the acid thus produced indicated that it was 

 probably propionic, possibly mixed with acetic and 



, Vii> 



Fig. 3. — {Drosera rotutidi/olta.) Diagram showing one of the exterior 

 tentacles closely inflected ; the tw« adjoining ones in their ordinary 

 position. 



butyric acids ; and the fluid, when acidified by sulphuric 

 acid, emitted a powerful odour similar to that of pepsin. 

 If an alkali is added to the fluid, the process of digestion 

 is stopped, but immediately recommences as soon as the 

 alkali is neutralised by weak hydrochloric acid. Mr. 

 Darwin believes that a ferment of a nature resembling 

 that of pepsin is secreted by the glands, but not until 

 they are excited by the absorption of a minute quantity of 

 already soluble animal matter ; a conclusion which is 

 confirmed by the remarkable fact observed by Dr. 

 Hooker, that the fluid secreted by the pitchers oi Nepetithes 

 entirely loses its power of digestion when removed from 



Fig, ^.— (Drosera rotundifoUa.') Diagram showing the distribution of the 

 vascular tissue in a small leaf. 



the pitcher in which it is produced. It is one of the 

 many extraordinary facts connected with this subject that 

 the tentacles of the leaves of Drosera retain their power 

 of inflection and digestion long after the separation of the 

 leaves from their parent plant. 



As might naturally be expected, salts of ammonia are 

 among the substances which have the most powerful 

 effect on the leaves of Drosera; but the excessively 

 minute quantities which are ^efficacious will probably bs 



