CHAPTER VI. 



THE RESIN-CANALS IN THE GUAYULE. 1 



THE CANAL-SYSTEMS. 



Because of the comparative interest of the facts involved it is here 

 proposed to summarize my observations on the origin, structure, and dis- 

 tribution of the resin-canals in Parthenium argentatum. The canals occur 

 in this plant in well-defined systems, 2 as follows: 



(a) Primary systems: 



i. In the cotyledons, the hypocotyl, and the root, a continuous 3 

 system. 



2. Independent of this, the systems in roots of secondary and 



higher order. 



3. In the cortex of the stem and in the dorsal moiety of the 



leaves, forming a continuous system. 



4. An independent 4 system in the dorsal moiety of the leaf. 



5. An independent 4 system in the ventral moiety of the leaf. 



6. In the pith of the stem: the medullary system. 

 (6) Secondary systems: 



1. Recurrently in the secondary leptome of the root and stem, 

 forming continuous concentric systems. There are no 

 transverse anastomoses between the several concentric 

 systems, such as occur in a laticiferous plant, Manihot 

 glaziovii, according to Calvert and Boodle (I.e.). 



PRIMARY CANALS IN THE ROOT AND HYPOCOTYL. 



These have their origin in the endodermis and are included within 

 it, as shown formany Compositae by Vuillemin, van Tieghem, Col (l.c ) ,and 

 Holm (1908). 



To be noted is a formation of a band of Caspary in the new walls aris- 

 ing in the cells destined to become a part of the canal. In the root there 

 are two groups, one group of two to four (or occasionally six) canals op- 

 posite each primary phloem bundle (plate 36, fig. 1). While this grouping 

 is generally true for the Tubuliflorae, the number of canals varies, e.g., in 



1 For a summary of the knowledge of the resin or oil canals in the Compositae 

 up to 1903, see Col (1903). An excellent historical sketch of the development of 

 our knowledge of organs of secretion of oil, resin, etc., is given by Tschirch (1906) 

 at p. 1095. 



2 In the usual sense as employed by, e.g., Vuillemin ( 18846), and by Calvert 

 and Boodle (1887). 



3 Vuillemin (18846) properly pointed out the independence of the canals of 

 the hypocotyl and epicotyl. He says: "les systemes secreteurs des deux membres 

 ou des regions differentes de m6me membre sont toujours distinctes." 



4 As to origin. 



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