CHAPTER XIII. 



PRIMARY ARRANGEMENT OF INTERCELLULAR 



SPACES \ 



Sect. 132. The air-containing, and sometimes water-containing intercellular 

 spaces have been described in Sect. 51, and in the paragraphs treating of the stomata, 

 the parenchyma, and the structure of the vascular bundle, and their arrangement was 

 described at the same time. Here it is only necessary again to bring forward the 

 fact already mentioned on p. 210, that all the air-spaces in question together form 

 a connected system of communicating tubes throughout the whole plant. Where 

 there are stomata this system opens first into the ' respiratory cavities ' below them, 

 and then through the slits themselves it communicates with the outside, and thus in 

 the terrestrial and swimming plants, which we have more especially under con- 

 sideration, it also communicates directly with the surrounding atmospheric air 2. 



Sect. 133. Of the i7iter cellular secretory reservoirs the short cavities have also 

 already been dealt with as regards their distribution, on p. 207. 



It therefore remains still to treat of the arrangement and course of the secretory 

 passages and canals, and at the same time to take into consideration many pheno- 

 mena of their structure, which were passed over before (comp. p. 206), with constant 

 reference of course to Sect. 50. 



The secretory passages traverse the members of the plant longitudinally at first 

 as prismatic tubes, which usually acquire a round or elliptical transverse section : 

 rarely they appear as more or less elongated sacs with both ends closed blindly, as 

 in the exceptional cases of Tagetes and Mammea, quoted on p. 201, and in many 

 Coniferae. In the great majority of cases they are in open communication throughout 

 the plant, forming a system of tubes, which branches and anastomoses — especially, 

 but not exclusively, at the nodes — and may send out blind, or also anastomosing 

 branches into the foliar expansions. 



Their arrangement in the members varies greatly according to the groups and 

 even the species, nevertheless it is regular and constant within each of these circles 

 of relationship. Besides those which appear constantly in one species or group of 

 dififerent rank, there are in many cases accessory passages, which may occur in 

 varying number according to the individual or species, or may even be absent, 

 e.g. leaves of Pinus, medullary passages of the Terebinthaceae, Coniferse, &c. 



* [Compare v. Hohncl, Verhaltniss der Intercellularraume zu den Gefassen, Bot. Ztg. 1879, p. 541 ; 

 also, Ueber Harz-raume im Kork-gewebe, Bot. Ztg. 1SS2, p. 161, and iiber gefassfiihrende Holzer mit 

 Harzgangen. Ibid.] 



^ Compare Sachs, Experimentalphysiulogie, p. 254. 



