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an abundance of gum, which 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 fistule, 
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 Cycadacez 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 atleast 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 Liége, analysed 
the leaves of Cycas revoluta, and ascertained that they con- 
tained, 1° Chlorohydrie 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 indu- 
rations of plants have always hitherto been ascribed to the 
presence of silex. From these facts M. Morren concludes 
that in Cycadacee 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. Zapériences et Observations sur la gomme des Cycadées 
in the Bulletin de Y Academie royale de Bruxelles, VI. no. 8. 
