Chapter X — 137 — Drosera 



underwent changes, shown to be due to digestion, and were found to 

 be free of bacteria, while similar pieces of material placed on wet moss 

 "swarmed with infusoria." 



Chemically the mucilage appears to be a sort of hydrocellulose, but 

 the seat of its secretion is not known. Like other cases of mucilage it 

 may be a product of an alteration of the cell wall, or it may be an 

 exudation from the protoplast. In any event it is permeated by other 

 substances in which its power of digestion rests — enzyme, acid, some 

 antiseptic substances, and latterly Weber has suspected the presence 

 of ascorbic acid. 



Small (1939) has advanced the notion that the mucilage is se- 

 creted only by the lateral cells of the gland, and not by the apical cells. 

 His evidence is seen in internal reflecting surfaces, stated to be present 

 at the apex and absent from the lateral cells, between them and the 

 mucilage. For my part I fail to find such reflecting surfaces. On the 

 other hand, if a piece of leaf with glands which have been thoroughly 

 wiped off with filter paper is placed in parafhn oil and carefully ex- 

 amined to find glands on which no trace of mucilage is visible, these 

 in the course of one to several hours will show numerous droplets of 

 mucilage oozing away from the surface as well at the apex as on the 

 sides of the gland (75— 14). Weber (1938) by means of sodium 

 oleate has demonstrated to his own satisfaction rods or streams of 

 mucilage radiating from the gland surface at every point. I have not 

 been able to confirm this. If the glands are watched under a binocular 

 dissecting microscope, in the course of a short time it will be noticed 

 that the surface of an opalescent mucilage drop is wrinkled longi- 

 tudinally, and by this time the surface of the drop has lost its glassy 

 look. It is evident that there is a surface concentration of some sub- 

 stance or substances. As one watches steadily, one sees an occasional 

 explosion on the surface as if some minute particle or droplet had on 

 arriving there from inside immediately spread over it. As the wrink- 

 ling progresses the drop becomes pear-shaped, the broad end above the 

 apex. With cessation of evaporation, the drop will assume its oval 

 form. The mucilage is a jelly-hke mass. If two glands with drops are 

 approached so that they touch and then are moved apart, the drops 

 will largely separate, adhering by only a slender thread. If a drop is 

 touched with a corner of filter paper at its basal margin and, on ad- 

 hering, the mucilage is pulled away upwards toward the gland apex, it 

 will tear away and extend asymmetrically from the gland apex. When 

 a drop is pulled out, it at first refuses to leave the gland. Only when 

 there is sufficient adhesion and pull, the whole mass, after a certain 

 amount of stretching, will pull away suddenly. These and similar 

 evidences indicate that the mucilage has a sort of structure. When 

 dry, it shows double refraction, but not when wet (Weber). It is not 

 so stiff a jelly as that of Drosophyllum, which pulls away readily in a 

 mass, but is otherwise similar. 



One other apparently trifling observation which I have made may 

 be mentioned here. I have noticed that, over the apical half of a 

 gland there are in the immediate vicinity of the gland surface minute 

 plaques of clear colorless substance not soluble in sulfuric acid, rounded 

 or sometimes angular in shape {15 — 10). Sulfuric acid dissolves the 



