CELLS— FIBRES— VESSELS. 



151 



vessel, like the rounds of a ladder ; this vessel is called Scalari- 

 form (L. scala, ladder). 



369. Lati- 

 ciferous Ves- 

 sels, or Ducts 

 (L. latex, la- 

 uds, any kind 

 of juice), are 

 formed by 

 lacunes (362). 

 At first they 

 are mere ca- 

 nals or pas- 

 sages between 

 the cells (Fig. 

 215, A, G). 

 Their office is 

 the carrying 

 of the special 

 secretion of 

 the plant, — 

 turpentine in 



FiG. 220. — A, Bpiral vessel of Melon {Cucvmu Melo). B, an- 

 nular vessel of do. D, moniliform pieve-duct of do, (dotted, 

 porous, punctate). C, scalariform vessel of Fern {Pleris aqui- 

 Una). 



the 



Fi8. 221.— A, section of young 

 Celandine (Chelidonium mtijiw) ; 

 showing the laticiferous canal 

 /. B, same, older; canal formed 

 into a. branching duct and de- 

 tached from the plant. 



Pine, milk in the Milkweed, etc.; 

 after a little, however, the secretion 

 often deposits a thin layer, which 

 forms a wall, and the canal simu- 

 lates a true vessel, or duct, which 

 may be detached (Fig. 221, B). 



370. Tissue-Systems. — Sachs proposes 

 to systematize tissues as follows : 



1. Fundamental, consisting of the un- 

 modified tissues found in all except the 

 lowest plants ; 



2. Epidermal, consisting of houndary- 

 cells (surface of root, stem, leaf), with 

 their appendages (hair, stomata, etc.) ; 



3. Fibro- vascular, consisting of the 

 thread-like masses abounding in the higher 

 plants. 



