152 ANATOMY OF THE GYMNOSPERMS 



From this it would seem that the fundamental tissue is the 

 most impressionable with respect to the development of these 

 structures, and that after it we have in the same order the 

 peduncle of the inflorescences and the wood of the young shoots, 

 to which latter category would also belong the development of 

 resin passages in fasciated stems, and such a sequence is pre- 

 cisely what we should expect from our knowledge of the relation 

 which the fundamental tissue bears to other structures. Accord- 

 ing to this conception the resin passages may appear in any part 

 of the woody structure where growth is sufficiently vigorous, 

 but such appearance would be temporary and indicative only 

 of a future course of development which has not as yet become 

 sufficiently well impressed upon the organism to form a perma- 

 nent feature of it. In other words, the tissue exhibits what in 

 other cases would be termed "sports." Such structural fore- 

 casts are well known and of frequent occurrence. As applied 

 to the development of tissues, no better example is afforded than 

 that shown by the central strand of mosses, which is generally 

 accepted as prophetic of the future vascular system in the spo- 

 rophyte, and they serve to suggest that the law of mutation as 

 proposed by De Vries finds expression in the evolution of internal 

 structures as well as in the development of external forms. Such 

 cases as Sequoia gigantea, which shows resin cysts in the wood 

 of the first year and nowhere else, being replaced later by resin 

 cells, appear to us to show that young and vigorous growth in 

 general, and therefore the growth ring of the first year, consti- 

 tutes a transitional zone within which many changes of structure 

 wholly apart from the strictly normal may arise ; and such a 

 law would similarly be applicable to the wood of peduncles. 

 This feature is manifested in the structure of the medullary ray, 

 the character of the tracheids as exhibited in transverse section, 

 the genesis of the bordered pits from spiral tracheids, and, in all 

 probability, also in the formation of resin passages in Sequoia 

 and Abies, as noted by Jeffrey. 



Changes of this nature are to be regarded as tendencies in 

 development in the direction of higher types of structure, whereby 



