256 M even's Report for 1839 on Physiological Botany. 



time, until it is absorbed in order to grease the cuticle (le 

 derme), so that it may not be wetted by the rain. As yet, it 

 has always been believed that the bluish wax-like substance 

 which is found on plums executes this office ; however he now 

 begins to believe that it is the aethereal oil which is formed 

 in the cells and then exudes. 



In the epidermal cells of the leaves of Colchicum autumnale, 

 M. Morren also found an oil (in spring), which did not move 

 in water as the oils in the two above-mentioned plants did, 

 and therefore it is probably a fatty oil ; M. Morren thinks that 

 this also exudes through the walls of the cells to the cuticle 

 and protects it from rain. In the oily seeds of Linum austri- 

 acum, Papaver spectabile and Brassica campestris oleracea, it 

 appeared to M. Morren that the oil was between the cells, 

 and that within them there was no trace of it. Finally M. 

 Morren mentions the large-stalked glands of Passiflora foetida 

 as secreting an aethereal oil on the surface. This is however 

 by no means uncommon, and is the case more or less with all 

 such stalked compound glands, and I have described the 

 same in the simple glands on the surface of Melissa offici- 

 nalis. 



In a short memoir M. Morren* has described the circum- 

 stances under which gum is found in the reservoirs in the 

 leaf-stalk of the Cycadea ; he remarks, that when one cuts off 

 the frond (wedel) of this plant so that more or less of the leaf- 

 stalks remain on the stem, the gum exudes on this surface 

 from the gum-passages ; and that from this it follows that the 

 gum ascends from the stem into the frond, but does not, as 

 physiologists have up to this time believed [? ?], descend from 

 the leaves into the stem. If the stumps of the leaf-stalks are 

 only two or three inches long, the gum exudes in the form of 

 a long vermicular body ; M. Morren observed it two or even 

 above four centimetres long ; in all experiments the gum was 

 seen to proceed upwards, but not downwards. I have repeated 

 several of these experiments and certainly found them to be 

 correct, but I have also made some others which perhaps like- 

 wise explain the phaenomenon. If a strong frond be bent into 

 pieces six to eight inches long, and these inverted in water, the 

 exudation of gum from the openings of the reservoirs is ob- 

 served ; but here it passes downwards, and it seems to me that 

 it may be explained by assuming an absorption of water by 

 which the gum is expanded, and thus a quantity is forced out of 

 the upper opening. When the gum exudes from the stumps left 

 on the stem, one may suppose that a quantity of the nutritive 



* Bulletin de l'Acad. Roy. de Bruxelles, vi. No. 8. 



