178 JOURNAL OF FORESTRY 



Wood-parenchyma 



The distribution of wood-parenchyma has been used by most in- 

 vestigators as a diagnostic criterion in the classification and identi- 

 fication of the wood of Dicotyledons. Sanio/ in 1863, distinguished 

 four principal types of distribution. In his "paratracheal" type, the 

 parenchyma is clustered about or jackets the vessels (fig. 5). In his 

 "metatracheal" type (fig. 7), the parenchyma forms tangential bands 

 or concentric layers. The vessels are embedded in these bands, when 

 the latter are of sufficient width, or, when this is not the case, they 

 adjoin them and are jacketed by a layer of parenchymatous cells. In 

 addition to these two types, he distinguished two others, in which the 

 parenchyma is not associated with the vessels. In the first of these, the 

 parenchymatous cells occur in bands or concentric layers. In the 

 second, they are diffused or scattered throughout the wood (fig. 1). 



Sanio's four types of parenchyma distribution were subdivided by 

 Krah- in 1883. This investigator recognized fifteen distinct types of 

 distribution. In recent years, much emphasis has been placed upon 

 the significance of three of these types of parenchyma distribution in 

 the construction of a natural classification of the higher seed plants.-^ 

 Furthermore, the distribution of parenchyma, owing to its supposed 

 constancy in large groups of plants, has been considered to be the 

 most reliable of all diagnostic criteria in the study of w'ood.* 



Certain large natural groups of the Dicotyledons are said to possess 

 '"diffuse" parenchyma, a type in which the parenchymatous cells are 

 scattered more or less uniformly throughout the wood (fig. 1). In 

 a second group of families the parenchyma is aggregated about the 

 vessels (fig. .")). This type of parenchyma distribution has been called 

 "vasicentric" and is the same as Sanio's paratracheal type. A third 

 group of families are said to possess wood-parenchyma only at the 

 end of the growth rings (fig. 4). This type has been called "terminal." 



The family Rosacae has been used as an example of a large natural 

 group of plants that possess diffuse parenchyma. This is true of such 

 characteristically north temperate genera as Pyrus, Sorbus, Crataegus, 



1 Sanio, Karl. Vergleichende Untersuchungen uber die Zusammensetzung des 

 Holzkorpers. Bot. Zeit., Vol. XXI, No. 50, p. 389, December, 1863. 



2 Krah, F. W. Ueber die Vertheilung der parenchymatischen Elemente im 

 Xylem und Phloem der dicotylen Laubbaume. Berlin, 1883. 



^Holden, R. Reduction and reversion in the North American Salicales. Ann. 

 Bot., Vol. XXVI, No. CI, p. 170, January, 1912 



^Forsaith, C. C. Some features in the anatomv of the Malvales. Am. ]rmv. 

 Bot., Vol. II, No. 5, p. 239, May, 1915. 



