15 



an abundance of gum, whicli flows from them freely in a 

 liquid state when wounded ; the author ascertained the cor- 

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

 matter takes place in special channels, i. e. in long fistulae, 

 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 

 experiments, that in Cycadacese 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 themselves to the trunk ; a suspicion eventually con- 

 firmed by chemical investigation. 



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

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

 tained, 1" Chlorohydric acid, probably combined with soda or 

 potash ; 2" Oxalic acid, probably free ; and S° Oxalate of lime, 

 forming the principal part of the solid exterior layer of the 

 leaves ; a very interesting fact, inasmuch as superficial indu- 

 rations of plants have always hitherto been ascribed to the 

 presence of silex. From these facts M. Morren concludes 

 that in Cycadacese gum is formed at the expense of the 

 starch of the stem, and that such a change is effected by the 

 action of the free oxalic acid secreted in the leaves. 



We are, therefore, to understand hereafter that gum is a 

 form of the nutritive matter of plants ; that, instead of being 

 the result of vegetable digestion, it is a principle created by 

 nature for their crude food ; that one at least, if not the prin- 

 cipal of the functional purposes for which starch is univer- 

 sally dispersed through the tissue of plants, is in order that it 

 may be every where ready for conversion into gum; and finally 

 that it is in the form of gum that starch passes through the 

 sides of the tissue in which its granules were originally gene- 

 rated. Mxperiences et Obsei^vatioyis sur la gomme des Cycadces 

 in the Bulletin de V Academie 7'oyale de BruxelleSf VI. no. 8, 



