INTERCELLULAR CANALS IN DICOTYLEDONOUS WOODS 433 



HamamelidacecB 



In Liquidambar onentalis and L. styraciHua there are normally no 

 secretory canals in the wood, though schizogenous canals occur in the 

 pith. As a result of injury, however, vertical canals may arise in the 

 wood of both species and produce a gum known as storax. The writer 

 has observed them in various specimens of our native species (red or 

 sweet gum), where they present the usual tangential seriation and net- 

 work. A specimen from Honduras shows them very prominently de- 

 veloped. 



Tschirch (4, p. 1204 et seq.) and Svendsen (5) investigated the 

 canals produced pathologically in these species. In the new wood in a 

 wound in L. styraciHua there were three concentric rows of canals em- 

 bedded in a zone of tracheidal-parenchyma. Their increase in size by 

 the breaking down of the surrounding cells was plainly noticeable, and 

 this process extended to include portions of the rays. No canals in the 

 bark or radial canals in the wood were observed. This is in agreement 

 with the present writer's observations, but contrary to those of Moeller 

 (6. p. 13), who noted secretory, cavities in the bark in communication 

 radially with vertical canals in the wood. 



RosacecB 



The presence of canals and cavities in the woods of the Prunoidese 

 is a matter of common observation. Their formation is ascribed to 

 gummosis or modification of the cell walls, not of normal tissues, as in 

 Acacia, but of previously differentiated groups of parenchymatous 

 cells, so-called "abnormal wood parenchyma." 



The specimens examined by the writer show vertical canals in tan- 

 gential series — small, but conspicuous, because of the dark red color of 

 the contents which test for mucilage rather than gum. The surround- 

 ing cells of the wood parenchyma and the rays are short, thick-walled, 

 and copiously pitted, as. for example, in Liquidambar. 



Lcf/ii}iiiiios(r 



Among the papilionaceous woods, gum canals appear in the older 

 xvlem of Hcrmiuicra clapJiroxylon (4, pp. 264-5), being placed verti- 

 cally in the wood and horizontally in the rays. 



In the Mimo.soide?e, the normal elements of the soft bast, pericycle 

 and wood of Acacia may undergo metamorphosis into gum (gum- 

 arabic) (2. p. 207), but no secretory canals in the wood have been re- 

 corded. 



