64. KOYAL SOCIETY OF CANADA 



the terminals of the ray are strictly uniseriate, and they hroadeii out 

 ahruptly in the immediate neighbourhood of the resin passage, a fact 

 which also holds true for Picea. In all these genera also, the elements, 

 including the epithelium cells, are all thick-walled, and the central 

 canal is small. In Pinus, on the other hand, the central canal is 

 large and commonly filled with thyloses; the epithelium cells are 

 thin-walled and large, while the neighbouring cells of the wood paren- 

 chyma are also large and thin-walled; the rays are generally much 

 broader than in the preceding genera, and, as a whole, the structure 

 shows a stronger tendency to broaden out from the terminals, a fact 

 which often finds expression in rays of strictly lenticular form. The 

 characteristics noted are so well defined as to permit a very exact 

 differentiation between Pinus on the one hand and the other three 

 genera, and on this basis it is quite safe to refer nearly, if not quite 

 all species of Pityoxylon to the genus Pinus. From these consider- 

 ations it is evident that 25 per cent of the Xorth American genera 

 possess fusiform rays as permanent and well defined characters, while 

 75 i^er cent are devoid of them. 



So far as I am aware, there is no existing species of Sequoia which 

 shows even a remote tendency to the formation of fusiform rays, but 

 in S. burgessii from the Lignite Tertiary of Porcupine Creek and 

 Great Valley, one of the most prominent structural features is the 

 occurrence of very well defined fusiform rays, the central canal of 

 which is filled with thyloses (Fig. 8). The unusually large size of 

 the resin passage at once serves to recall the large, structurally similar 

 and similarly situated mucilage canals of Cycas revoluta. As already 

 noted, no suggestion of such structures is to be met with among the 

 North American Coniferae, but in Araucaria glaujca I have found rare 

 examples of a similar development, though in all cases so far observed, 

 the resin passage has been but imperfectly organized. That this 

 character is wholly exceptional in the genus Sequoia as a whole, can- 

 not be doubted, and it is unknown more recently than the Eocene. 

 How far back in geological time it may have been developed, it is 

 at present impossible to say, but it gives conclusive proof that in 

 Sequoia burgessii we have the culmination of a short side line of 

 development probably within early Tertiary time. 



Thyloses in the Besin Passages. — According to generally accepted 

 views, the appearance of thyloses indicates a local, pathological con- 

 dition ^ since they usually arise as stated by De Bary,- in old or dam- 



* Agricult. Ledger, Calcutta, 1901, No. 8, 129, 180; Jn'l. Bot., X., 1872, 321-323; 

 Ward. Timber and some of its Diseases, 1889, 75; Hartig. Lehrb. d. Baum- 

 krankheit, 1882, 133. 



^ Comp. Anat., 170. 



