144 PART II. THE INTIMATE STRUCTURE OF PLANTS. [ 30. 



the deeper layers of the cuticularised cell- wall (e.g. mucilaginous 

 hairs [colleters] on the buds of many Phanerogams, resinous hairs 

 generally; Fig. 108). 



30. General Morphology of the Tissue-Systems. 



When a form of tissue constitutes a complex which extends con- 

 tinuously throughout the body of a plant, or over considerable 

 areas, it is spoken of as a tissue-system, for instance, a laticiferous 

 system, a resin-duct system, a sieve-tube system, etc. ; or a more 

 elaborate system may be produced by the combination of two or 

 more systems : for instance, the sieve-tube system and the tracheal 

 system taken together constitute the vascular tissue- system. Fur- 

 ther, by the study of the anatomy of fully-developed parts some 

 idea can be obtained of the relative morphological importance and 

 arrangement of the tissue-systems. Thus, confining attention for 

 the present to the sporophyte of the Vascular Plants (i.e. Pterido- 

 phyta and Phanerogams), it is found that some of these tissue- 

 systems, such as the laticiferous system and the resin-duct sys- 

 tem, are present in certain plants only. Since they are absent in 

 the majority of the plants under consideration, it is clear that 

 these two tissue-systems can only be of secondary importance. 

 On the other hand it is clear that the tissue-systems which are 

 present in all these plants and in all parts of them, must be of 

 primary importance. Observation shows that this applies to 

 three tissue-systems. It is found, first of all, that all these plants 

 and their parts (at any rate when young) are covered at the sur- 

 face by a definite membrane consisting of (usually) a single layer 

 of cells constituting the Tegument ary Tissue- System (Fig. 109 e). 

 It is found secondly that tracheal tissue and sieve-tissue, either 

 separate or closely associated, are distributed in strands, termed 

 vascular bundles (Fig. 109 /), throughout the internal structure, 

 constituting the Vascular Tissue- System ; and it is found, finally, 

 that the rest of the structure of the plant is made up of tissue, 

 largely parenchymatous, but usually to a certain extent prosen- 

 chymatous, which constitutes the Fundamental or Ground Tissue- 

 Si/stem (Fig. 109 # #). 



The other tissue-systems are subordinate to these three prin- 

 cipal tissue-systems, and are distributed throughout them; for 

 instance, the mechanical tissue-system (stereom), including collen- 

 chyma and sclerenchyma, is developed as well in relation with the 

 vascular as with the fundamental tissue-system ; and, similarly. 



