50 BOTANICAL GAZETTE [yuLy 
in Picea excelsa vars. monstrosa, conica, elata, pendula, and pyra- 
midalis. Finding them characteristic of these varieties of the com- 
monly planted Picea excelsa, it was decided to extend the studies to 
other species. Through the courtesy of Professor JAcK, of the Arnold 
Arboretum, I was able to secure carefully identified green material 
of seventeen species of American, Asiatic, and European spruces. — 
Thin serial sections of this material showed that the presence of wood- — 
parenchyma upon the outer surface of the summer wood is a charac- 
teristic condition for Picea. Its occurrence, however, is extremely 
sporadic. In any given fragment of wood the cells may or may not 
appear, and while usually occurring very infrequently, may at am 
time appear in large numbers. These cells appeared more numeé: 
ously in the European and Asiatic species, and in Picea sitchensts 
Carr. and Picea Parryana Sarg. of the American species. In the 
spruces from the northeastern United States they could be made out © 
only with difficulty. S 
The extremely variable occurrence of wood-parenchyma is also 
characteristic of Larix and Pseudotsuga, for though usually occurring — 
numerously upon the outer surface of the summer wood, in mam 
specimens they may be very infrequent or nearly absent. | 
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SEPTATE TRACHEIDS 
In the three genera of the Pineae just mentioned septate tracheids 
occur with the parenchyma upon the outer surface of the year’s growth. 
In Picea they are usually more numerous than the wood-parench: 
and occur where wood-parenchyma is not developed. In Larix and- 
Pseudotsuga the parenchyma usually predominates. There is 4 
clear gradation shown from tracheid to parenchyma in these geneté. 
Frequently one may observe in the same section a septate tracheid, 3 
tracheid partly septate and partly parenchymatous (fig. 4), and 
series of resin cells, together having the form of a tracheid. Ino 
words, the various steps by which tracheids have been modified 
form parenchyma are clearly shown. In support of these stateme 
it may be well to add that primitive woods were composed enti 
of tracheids and medullary parenchyma, and that only in the hig 
8ymnosperms do we see the development of wood-parenchyma, 
upon the outer surface of the summer wood, and later throug 
