EXTRACTS from foreign periodicals. 151 



coloured in the same manner. A thickness not its own is therefore sometimes 

 attributed to the substance. The same precaution must be observed in all the 

 woods of Dicotyledons. In Coniferce, for instance, the lines of separation be- 

 tween the substance and the cells are much less cut off than those between the 

 internal and external layers of these cells. It is, therefore, easy to make a 

 mistake. 



In order clearly to observe this matter in the cellular tissue of wood, the hard 

 tropical woods, or our Box-tree, should be selected. It is much more difficult to 

 detect it in the majority of our indigenous trees, because the cells are there 

 extremely small, and closely connected. 



It is well characterised in the elongated cellular tissue of the bark and 

 petioles of the greater part of phanerogamous plants, as the Elder (Sambucus 

 nigra.) 



In parenchyma, or rounded cellular tissue, the cellular matter is so small in 

 quantity that it generally eludes observation. Hence the existence of passages 

 which are but empty spaces caused by the scarcity of this -substance. It is, 

 however, still obvious in tough leaves, as the Laurel (Laurus nobilis). The 

 facility with which the cellules can be separated sufficiently proves its existence 

 in all rounded cellular tissue, even in cases where its extreme tenuity and 

 transparence prevents its being distinctly seen. 



The albumen of many Monocotyledons contains it, whether between the cells 

 or at the surface, and it covers them with a homogeneous layer (as in Lilium 

 martagori). 



The external membrane which M. Brongniart has detached from the cuticle 

 by maceration, is but a homogeneous layer of the same substance, which fills 

 not only the intervals of the cells of the cuticle, but also covers them on the 

 outside with this pellicle. 



Lastly, the external envelop of grains of pollen is almost always composed 

 entirely of intercellular substance. 



These and other observations illustrate the important part which the substance 

 under consideration performs in the vegetable kingdom. Its study, carried still 

 further, will one day lead to interesting results on many physiological points. 

 The theory of the ascent of juices by the intercellular passages is already rendered 

 little probable, since these passages are only exceptions to the normal state of 

 the plant. 



This substance is semi-fluid, sometimes hard and solid, but never fibrous, 

 transparent, perfectly homogeneous, and almost always very hygroscopic. Its 

 chemical properties appear to be analogous to those of the cellular tissue which 

 it envelops, and vary, consequently, according to the species and the organs in 

 which it is observed. But M. Mohl has not yet distinctly described its chemical 

 nature and physical properties. 



