CHAPTER IX 



RESIN PASSAGES 



STRUCTURAL 



Our studies of the resin cell have shown how peculiar aggre- 

 gates of these structures lead in a natural way to the organiza- 

 tion of resin passages, the structure of which it is now necessary 

 to discuss somewhat in detail, and in doing so it will be most 

 profitable to have reference to (i) the primitive form, (2) the 

 intermediate form, and (3) the advanced or fully organized form. 



The primitive form of the resin passage is to be found in 

 Tsuga, Abies, and Sequoia, and inasmuch as within these genera 

 they exhibit differences in organization which correspond approxi- 

 mately to the sequence given, it will be necessary to discuss 

 them somewhat in detail, with special reference, however, to 

 Sequoia. This genus possesses special interest with respect to 

 the occurrence and organization of secretory reservoirs, since it 

 is in all probability not only the most ancient genus in which 

 such structures occur, but it is, so far as I am aware, the only 

 genus affording special data with respect to important varia- 

 tions of structure and mode of occurrence. Being also, on the 

 whole, the most primitive of the three genera, it may be dealt 

 with first. 



In Sequoia sempervirens the secretory reservoirs occur in 

 rows within the initial layers of the spring wood, 1 and they 

 therefore lie exactly on the outer face of the summer wood of 

 the previous year. Within this row the reservoirs are contigu- 

 ous, and in many cases they become confluent so as to form a 



1 The apparent occurrence of these structures in the summer wood is due to the 

 presence of two growth rings of very unequal degree of development, the outermost 

 of which may have only one or two rows of tracheids in addition to the resin cysts. 



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