CHAPTER VII. 



APPENDIX. INTERCELLULAR SPACES. 



Sect. 49. Between the elements of mature tissue there are often cavities, which 

 are grouped under the term intercellular spaces. 



These arise in two ways in the original masses of cells, which, at least when in 

 the state of meristem, are always in uninterrupted connection. Firstly, by separation 

 of permanen/ tissue-elements, as the result of their unequal surface-growth in different 

 directions, the original common walls splitting, while the common limiting layer which 

 was originally present is — perhaps always — dissolved. Secondly, by disorganisation, 

 dissolving, or in many cases rupture of certain transitory cells, or groups of cells, 

 which are surrounded by permanent tissues. We may call the first mode of origin 

 schizogenelic, the second lysigenetic, and, if a special term must be adopted for the 

 mechanical rupture, it may be called rkexigenetic. 



According to the stage of development at which the formation of intercellular 

 spaces takes place, one may, with Frank ', distinguish as protogetietic those which are 

 forrned on the first differentiation of tissues, and as kysterogenetic those which appear 

 subsequently in old mature tissues. 



According to their contents intercelluJar spaces fall into two categories. The 

 first are filled with bodies or mixtures of the same sort as the secretory sacs treated 

 of in Chap. Ill, or the secretory cavities of the epidermis ; they are nearly related to 

 these anatomically and physiologically, and spaces of these two categories not un- 

 frequently appear even to act as substitutes one for the other. They may be designated 

 secretory intercellular spaces, or intercellular secretory reservoirs. In treating of them 

 reference has often to be made to the other, not intercellular, secretory organs. 



The others contain from the very first only air, or in rare cases water. They 

 form together a special ventilating apparatus for the tissues. The stomata of the 

 epidermis (p. 34) are a part of this apparatus ; they are a special case of schizogenetic 

 and protogenetic spaces, which usually contain air, but also water in the special cases 

 mentioned. 



The same intercellular spaces rarely take part in both functions. Thus in the 

 parenchyma of Lysimachia Ephemerum, where the fixed, red, resinous secretion, to be 

 more accurately described below, partly covers the wall of the cells bordering on the 



' Beitr. zur Pflanzenphysiologie, p. loi. 



