TISSUES AND SIMPLE ORGANS. 



75 



represents their appearance during the summer. A noteworthy 



change takes place in these sieve-plates during the winter : the 



entire sieve-plate septum becomes swollen 



and softened on the two surfaces, similar 



to a gelatinous cell-membrane (" callus "). 



This callus evidently serves to close the 



openings of the sieve-plate in the winter,' 



The following table gives the earlier and 



^s1evft7be''wUh °'fou? ^^^^r names of cell-forms which were in- 



sieve-plates. eluded in the old expression " vascular 



(Diagramatic, after de Bary.) , ,, „ -j-. ~ n.,- ^ 



bundle. it forms a fitting conclusion to 

 the discussion of the cell-forms enumerated in this chapter. 



Haberlandt's /Synopsis of Cell-forms^ Slightly Modified hy the 



Author, 



r 



Mestome 

 \ (Scliwen- 

 dener) 



Leptome (Haberlandt) 



Sieve-portion(de Bary), 

 unluckily named 

 ' ' soft bast' ' by some 



Bast ^ 



f Sieve-tubes and con- 

 ducting-cells 

 Cambiform 

 Longitudinal bundle- 



parenchyma 

 Medullary - ray pa- 

 renchyma 



>■ Phloem (Nageliy 



HadroTne (Haberlandt) 



Vascular portion (de 

 Bary) 



Vessels and tra- 

 cheids 



Woody parenchy- 

 ma 



Ray-parenchyma 

 Libriform _, 



Xylem (Nageli), 

 usually called 

 " wood." 



Bast and libriform really do not belong to the ' ' mestome ' ' ; 

 they form (inclusive of coUenchyma) an independent tissue-system, 

 the stereome (mechanical system). 



A small conducting system which is not widely distributed, but 

 is Kmited to certain plant-families, has not yet been touched upon, 

 but will now be briefly discussed. This is the laticiferous tissue 

 ("milk-tubes"). 



De Bary, Comparative Anatomy. 



