THE FOOD OF PLANTS. 



105 



encloses colourless cell-sap, in which, however, the variously 

 shaped aggregations, in the form of intensely red-coloured masses, 

 ju (' rasy to make out. These aggregations have a wall, the nature 

 of which has not yet been accurately determined ; at least, I do 

 not consider the statements of de Vries on the subject fully con- 

 clusive. Within them cell-sap is present. In the production of 

 these structures the cell-sap, originally uniformly distributed in 

 the cell, must have separated into two parts, one very rich in pig- 

 ment, the other clear like water. How this comes about is not yet 

 adequately determined. When Ammonium carbonate is brought 

 into contact with tentacles of Drosera, processes of aggregation are 

 also exhibited, in which, however, precipitations of proteid have 

 been observed (H. de Vries). 



Plants of Dionaaa muscipula to be employed for physiological 

 experiments are most conveniently cultivated on pieces of wet 

 peat under a bell-glass. I shall not here consider the mor- 

 phology of the leaf of Dioneea, but simply describe carefully a 

 few easily conducted experiments. If the filaments present on 

 the upper side of the Dionaea leaf are touched, say with a small 

 splinter of wood, the leaf at once closes up. Soon, however 

 (in my experiments at 



the end of twenty-four \ \ \ I I / / / 



hours), the wings of 

 the leaf w r ill be found 

 to have expanded 

 again. If fragments 

 of raw meat are placed 

 on a Dionasa leaf so 

 as to touch the fila- 

 ments, there is an. im- 

 mediate closing move- 

 ment. In this case, 

 however, the leaf re- 

 mains closed for a long time (in experiments conducted by me 

 for more than eight days), thus differing from leaves induced to 

 close by placing non-nitrogenous bodies on their surface (frag- 

 ments of glass, paper pellets), or by simply touching their 

 filaments. When a Dion sea leaf, on which have been placed 

 fragments of meat, opens again, it is seen that the meat is more or 

 less disorganised and dissolved, this result being due to a secretion 

 produced by glands present on the upper side of the leaf. This 



FIG. 31. Leaf of Dionsea muscipula, expanded and 

 seen from the side. (After Darwin.) 



