Chapter VIII — 103 — Drosophyllum 



In 1894 came Meyer and Dewevre. They managed to collect 1.6 

 grams of mucilage and investigated it. It was stiff, clear, had the odor 

 of honey and was strongly acid. It contained no free reducing sugar, 

 but on heating with HCl it reduced Fehling, and gave a weak red 

 color with thymol and H2SO4 (indicating polysaccharides). The 

 presence of a sugar was indicated by a yellow coloration with chlor- 

 zinc-iodide as also its precipitation by lead acetate, by barium hydrox- 

 ide and by alcohol. No proteins were present. It was poor in salts, 

 only Ca being present. No K, phosphates or nitrates were found. 

 The acidity was due to a non-volatile acid, and not to formic acid, as 

 Goebel had held. These authors verified Darwin's observation that 

 the sessile glands secrete only on stimulus by a protein. Insects are 

 attracted both by the odor and by the gHstening of the droplets of 

 mucilage. They recorded observations also which indicate that there 

 are two periods of activity in the plant, (i) From the beginning of 

 vegetative activity to the beginning of seed ripening (from Jan. 15 to 

 May 15, in the greenhouse). During fruit ripening the leaves begin 

 dying from apex to base and the glands do not secrete vigorously. The 

 soil must be kept "dry" during this period. (2) After fruit ripening is 

 complete (Aug. i to Oct. 15) secretion and odor are both strong, es- 

 pecially in sunny weather. The experience of Darwin was again sub- 

 stantiated in finding that coagulated egg albumen, meat and fibrin 

 were acted upon, especially if well smeared with mucilage and placed 

 on the sessile glands. The time necessary for complete digestion was 

 about the same as in Darwin's experience. Goebel's figures were 

 criticised as being too low but an error of proofreading may have 

 crept in, rather than, as is suggested, incorrect observation. It was 

 found that very small fragments of albumen were attacked in the 

 mucilage of a stalked gland and completely digested in 7 days. If large 

 bits were imposed, they absorbed the mucilage, and damage might re- 

 sult to the gland in consequence. No diastase was found. Bacteria 

 were never found and it was clear that the mucilage, as Goebel said, 

 is antiseptic. 



Franca (1925) gave a general account of the plant, and studied 

 especially the cytological changes which he observed in the glands 

 during digestion and absorption, using both Hving material viewed 

 microscopically, and fixed material stained with iron haematoxyhn and 

 fuchsine, etc. He found evidence that the two courses of the glandular 

 cells (the outer and second) have different functions, that the outer 

 course is secretory only, the inner both secretory and absorptive. The 

 sessile glands have only the power of secretion. This evidence con- 

 sists in the cytological appearances observed during digestion and ab- 

 sorption. Changes of the bright red color in the glands to a deeper, 

 much darker shade, had been noted by Darwin. When such glands 

 are examined, the cells of the outer layer of the gland are seen to have 

 remained unchanged, while those of the second layer are now charged 

 with large black granules. These rise to a maximum some hours after 

 the glands have been suppKed with muscle fiber. Some similar granules 

 are found also in the more distal short cells of the stalk of the gland 

 and finally in approximate leaf tissues. Such dark granules are seen 

 when an insect has been captured, but only in the deeper gland cells. 



