1914] CURRENT LITERATURE 83 
The resin canals, both horizontal and vertical, are said to be tylosed gener- 
ally. Since there is no evidence presented that they were ever open, this is 
probably not a true tylosed condition, but rather the solid condition of the 
ancestral forms, a condition which is very prevalent in the older fossils. It is 
to be noted also that in the two forms which Miss HoLpDEN considers more 
primitive than P. protoscleropitys, resin canals are said to be filled with thick- 
walled cells. In one of them, P. folioswum, where the resin ducts are very 
numerous, they are frequently in tangential groups of three or four. The fact 
that tangential series of resin canals can be revived in the living pines by injury, 
and that such traumatic resin canals are usually solid is in agreement with the 
fossil condition, and indicates that the resin ducts of the pines were ancestrally 
of this type. 
In all three forms, the pits are usually uniseriate and scattered. In P. 
protoscleropitys, Miss HOLDEN speaks of the terminal pits of the tracheids as 
eing sometimes “closely approximated and flattened by mutual contact.” 
She has not described this pitting in the other two. No bars of Sanio have 
been observed except in the former, the most specialized form. The ray pitting 
of its tracheids, too, shows a tendency toward the formation of “Grosseiporen,” 
while theirs is piciform, the more primitive condition. Tangential pitting of 
the summer wood is absent in P. protoscleropitys, but present in the others. 
She says that this confirms “the conclusions of JEFFREY and CHRYSLER that tan- 
gential pitting is a primitive feature now lost in the more highly specialized hard 
pines.” She has evidently overlooked SrRASBURGER’S previous statement of 
this conclusion (Hist. Beitrage 3:9. 1891), as did JEFFREY and CHRYSLER 
themselves. 
iss Hotpen’s P. protoscleropitys has the sculptured ray tracheids of a 
hard pine, while the other two forms have no ray tracheids. She has looked in 
the former for verification of the mode of origin of ray tracheids proposed by 
THOMPSON," from vertically elongated tracheary elements, but on finding none 
disparages the correctness of THompson’s work, stating that it is “unlikely that 
this hypothesis is correct.” She has evidently not understood the problem, 
for the form in which she looked for evidence is, by her own statement, a special- 
ized one’in this very feature. Again, she was dealing only with the stem, while 
THoapson worked chiefly with the more conservative organ, the root. More- 
over, the recent investigations of CHRYSLER,” who has thoroughly worked over 
€ ground from the standpoint of the phloem, have confirmed THompson’s 
conclusion. He found the evidence in the root so much clearer than in the stem 
that he says he soon discontinued the study of the latter.—R. B. THomson. 
*THomPson, W. P., The origin of ray tracheids in the Coniferae. Bor. Gaz. 
59:10I-116. 1910. 
“ CuRyster, M. A., On the origin of erect cells in the phloem of the Abietineae. 
Bor. Gaz. §6:36-s50. 1913. 
