CELL COMMUNITIES: A CHAPTER ON TISSUES 



81 



Like the vessels last mentioned, the 

 laticiferous vessels are closely allied 

 to the sieve-tubes, consisting of closed 

 tubes, cylindrical or angular in shape, 

 and usually with thin, transparent 

 walls. They are formed by the union 

 of cells, but not necessarily (and here 

 they differ from most vessels) by the 

 union of a single row of cells. They 

 appear to be bound by no rule of 

 growth, so that some very irregular 

 vessels are often seen which branch 

 out in all directions and form a copious 

 network, with free intercommunica- 

 tion. Their presence is limited, how- 

 ever, to a small number of plants ; 

 for the milk-sap of many latex-yield- 

 ing species is not contained in vessels, 

 but in long, branched, simple cells. 

 The Euphorbias (fig. 107), to which the 

 Spurges and South African Tapioca- 

 plant belong, abound in these cells. 



We come now to tissues. The 

 sections figured (106-114) preclude the 

 necessity of any very detailed descrip- 

 tions. They show four kinds of tissue ; 

 but some courage is needed to declare 

 their names. 



The tissue of cells shown in fig. 108 

 is known as 



PARENCHYMA 



(Greek parenchuma, the spongy sub- 

 stance of the lungs), and this is the 

 general name of tissues the cells of 

 which are arranged in rows, and 

 which are fairly equal in their dimen- 

 sions, being almost as long as they 

 are broad. 



The tissue depicted in fig. 109 is 

 distinguished as 



PKOSENCHYMA 



(Greek pros, beside ; encJiuma, some- 

 9 





Photo 6y] [/?. Step. 



FIQ. 112. LARCH (Larix europceus). 



The shoots grow downwards, but the cones bearing 

 the seeds stand more or less erectly. 



