The Resin-Canals in the Guayule. 169 



MEDULLARY CANALS. 



IN THE EPICOTYL. 



All medullary canals are protogenic. Secondary ones do not occur. 

 The typical number of canals is not established for ten or more internodes, 

 this probably being variable. In field seedlings, or ones of slow growth, 

 the distance from the cotyledonary to the tenth node is very short, and 

 the particular behavior of the canals is difficult to determine. Etiolated 

 seedlings, therefore, throw more light on the matter, though it can not be 

 asserted that the behavior in such is always normal, e.g., when the canals 

 end blindly above, as they have been observed to do, instead of continuing 

 to the apex of the stem. These short canals may, perhaps, be regarded as 

 " poches secreteurs" the pockets in which Col sees reduced canals. The 

 following notes, based upon a series of sections made of a seedling about 10 

 cm. tall, with 16 nodes, show that the definitive condition is established 

 only at length, even the sixteenth node being sometimes reached before 

 the full complement of canals occurs. 



No canals below the fifth node. 



At fifth node, one canal passing into bud. 



Fifth internode, lower part, no canals; upper part, four canals. 



Sixth node, one of these into bud. One branches, making four enter- 

 ing lower part of sixth internode. 



Upper part of sixth internode, two canals; higher up, three, one send- 

 ing a branch to bud of the seventh node. 



Seventh node. At this level two more canals, making five to enter 

 the 



Seventh internode, in which one ends, leaving four in middle part. 



Eighth node, four canals, of which one branches into bud. 



Eighth internode, two canals in middle part. One branches, making 

 three to the 



Ninth node, at which the bud receives a branch. 



Tenth node, four, one branching to bud. All but one end blindly, so 

 that the 



Tenth internode receives only one canal. Two more arise, making 

 three for the 



Eleventh node. One passes without branching into the bud, leaving 

 two to enter the 



Eleventh internode. One of these ends, so that one canal reaches the 



Twelfth node, at which one more arises bv branching, and enters the 

 bud. 



Twelfth internode receives one, which ends blindly on reaching the 



Thirteenth node, where a new one arises and passes into the bud. 



Thirteenth internode has no canals in the lower part. 



Fourteenth node, one canal arises and passes into the bud. 



Fifteenth and sixteenth internodes, two canals in each. 



Despite the irregularity in numbers, and also in position, it is clear 

 that the canals in the pith have peculiar relations with the nodes. When 

 one arises it does so in connection with the development of an axillary bud, 

 and either enters it or sends a branch to it. This is to be inferred also 



