538 PROCEEDINGS OF THE AMERICAN ACADEMY. 



other, that the resin canals in the case of the former and the resini- 

 ferous parenchyma in the case of the latter, do not appear in the first 

 annual ring of the seedlings but only in the first annual increment of 

 older and more vigorous axes. In the case of Agathis it is clear from 

 the fossil data, that we actually have a harking back to ancestral 

 phenomena, presented in the exT;inct forms as shown above. In Abies 

 and Sequoia we can only infer that their ancestors had resin canals 

 in accordance with accepted principles of biological science. It seems 

 clear also in both types of illustration, that we have in the case of 

 the living representatives, to do with reduction phenomena. The 

 fact that Abies and Sequoia on the one hand and Agathis on the other 

 hand are degenerate descendants of stocks once more vigorous and 

 richly endowed, doubtless furnishes the explanation of why the recapi- 

 tulationary phenomena in connection with the first annual ring make 

 their appearance not in the seedling; but only after the plant has 

 attained the reproductive age. 



Figure /, Plate 3, illustrates the conditions found in connection with 

 the parenchyma of a wounded root of Agathis ausf rails. It is to be 

 noticed that most of the parenchymatous cells are thick-walled and in 

 some instances strongly pitted. This figure is to be compared with 

 Figure c, Plate 1, which shows the normal condition of the cone axis. 

 Here both the rays and parenchyma are thick-walled on the side nearer 

 the pith. In the case of A. ausfralis the adult stem, when injured, 

 in contrast to the root does not form thick-walled wood parenchyma 

 but only thin walled elements. That this is the case is demonstrated 

 by Figures a and b, Plate 4, which show the injured stem wood of 

 A. australis in transverse and longitudinal section. Thin-walled 

 parenchyma can be seen in each case. 



Figures c and d, Plate 4, show the transverse and longitudinal views 

 of the heart wood of A. australis, illustrating the presence of resinous 

 exudations in the tracheids of the wood immediately adjacent to the 

 rays. In the longitudinal view the relation of the exudation to the 

 ray cells is particularly well seen. Penhallow has compared these 

 transverse septa, resulting from substances poured out by the ray 

 cells into the tracheids with the trabeculae of Sanio. They ha\'e in 

 reality of course nothing to do with these structures. ^^ Lignier has 

 described the thickening up of the tracheids adjacent to the rays in 

 certain Araucarian woods from the French Jurassic. It seems entirely 

 probable that he has mistaken resin filled tracheids for thick-walled 



12 Penhallow, North American Gymnosperms, Boston (1907), pp. 53-58. 



