FUNCTION.] GUM. 281 



and the cellular part of endogenous stems, it forms the prin- 

 cipal part of the mass. In such cases it is ready to be 

 chemically changed at a fitting period, and to become the 

 food of the germinating embryo, or of young stems and 

 leaves. According to M. Payen, it is enabled to execute this 

 important purpose, by virtue of its gradual solution by water 

 and diastase, which convert it into dextrine and sugar, and 

 thus render it capable of percolating the surrounding tissue, 

 and passing from chamber to chamber of parenchym. 

 (Memoir e sur V Amidon, p. 131.) 



In his investigation of the anatomy of Cycads, Professor 

 Morren arrived at a fact of great interest in Vegetable 

 physiology. It is well known that all these plants yield an 

 abundance of gum, which flows from them freely in a liquid 

 state when wounded ; the author ascertained the correctness 

 of Professor Meyen's statement, that the flow of such matter 

 takes place in special channels, i. e., in long fistulse, whose 

 walls are built up of cellular tissue. It is usually supposed 

 that gum is a secretion from the leaves of plants, and that it 

 consequently flows from above downwards ; it has been even 

 compared to the blood, and regarded as the most pure, and 

 most essential part of their nutritive matter. Professor 

 Morren has, however, proved by some well conducted expe- 

 riments, that in Cycads at least, the gum moves from below 

 upwards, and that it arises in the stem, whence it mounts 

 into the leaves. The author therefore suspected that gum is 

 an ulterior elaboration of the starch lodged in the trunk, and 

 that such elaboration is excited, or brought about or at least 

 assisted, by some acid, probably supplied by the leaves them- 

 selves to the trunk ; a suspicion eventually confirmed by 

 chemical investigation. 



M. de Coninck, Professor of Chemistry at Liege, analysed 

 the leaves of Cycas revoluta, and ascertained that they con- 

 tained 1 Muriatic acid, probably combined with soda or 

 potash; 2 Oxalic acid, probably free; and 3 Oxalate of 

 lime, forming the principal part of the solid exterior layer of 

 the leaves ; a very interesting fact, inasmuch as superficial 

 indurations of plants have always hitherto been ascribed to 

 the presence of silex. From these facts M. Morren concludes 



