24 



EDWARD C. JEFFREY ON 



the female cone. This feature is the more remarkable since resin canals are absent 

 ordinarily in the woody tissues of the Sequoias and are replaced by resin cells of 

 the usual Cupressineous type. This characteristic of the first annual ring of vigorous 

 branches of mature trees of Sequoia gigantea must apparently be interpreted as ances- 

 tral, since it is paralleled by the presence of a similar feature in the reproductive axis. 1 

 The condition of reduction from a more luxuriant ancestry also explains why the 

 resin canals in question are not found in the seedling in the first annual ring. 

 Apparently there must be a considerable accumulation of nutritive capital before 

 the species under discussion is able to reproduce the ancestral conditions even in 

 the first annual ring. It may be set down then as a rule, which in the future will 

 doubtless receive numerous exemplifications, that in forms which have clearly suffered 

 vegetative reduction the reappearance of ancestral conditions may be delayed to the 

 first annual ring of the more vigorous shoots of the adult. 



A further general principle of comparative anatomy, which is beginning to be estab- 

 lished, is that ancestral conditions may be recalled by appropriate experimental conditions 

 Where there has been reduction from a more luxuriant ancestral type, experimental con- 

 ditions, which bring about a greater determination of nutrition to the parts in question 

 are apt to cause a reversion to the ancestral structure. It has been shown by Jackson 

 ('99) that this is often true of the external form. In the case of Sequoia, as I have 

 pointed out in the first memoir of this series (Jeffrey, : 03) , injuries to the phloem and 

 the cambium, which bring about a damming up of the products of assimilation in the 

 region of the injury, cause a hypertrophy of the woody tissues. In this hypertrophied 

 wood more or less typical resin canals occur, similar to those found in the first annual ring 

 of certain branches and invariably in the woody tissues of the female cone of S. gigantea. 

 It is apparent that experimental morphology is likely in the near future, to receive from 

 botanists the same attention that it has already begun to enjoy in the hands of the 

 zoologists. 



The phylogeny of the Abietineae. — The enunciation of general principles briefly 

 attempted in the foregoing paragraphs will serve a useful purpose in the discussion of the 

 phylogenetic relationships of the Pineae and Abieteae. In the latter group, it has been 

 noted in the descriptive part of the present memoir that resin canals are generally absent 

 from the woody tissues of the root and shoot. Exceptions to this statement occur in 

 the following cases. In the genus Abies, resin ducts have been found in the wood of 

 the cones of A. grandis, A. magnifica, and A. apollinis. In A. magnified (as in 

 Sequoia gigantea) these are also in the first annual ring only of vigorous vegetative 

 branches of mature trees. Resiu ducts also are found invariably in the primary wood 



1 Kadais ('94) has also noticed this feature of the cone in S. gigantea. 



