The Resin -Canals in the Guayule. 173 



low the second node. The other three end blindly before they reach the 

 node, so that the following internode has none, as above said. It is evi- 

 dent that we find here a sort of morphological indecision, as if the stem 

 were trying to retain its stem character, and still being gradually over- 

 come by the tendency toward changing into a peduncle. The same prepa- 

 rations show also the formation of chlorenchyma strips in the cortex of 

 the peduncle sector, nearly down to the base of the first internode below 

 the peduncle. 



The axillary bud of the third node below the peduncle receives a 

 single branch from one of five canals, the normal number, present in the 

 internode below. Here, therefore, the complete stem structure is first 

 met in our descent from the peduncle. It would be interesting to specu- 

 late on the internal causes which result in diverting the canals, en masse, 

 from the chief shoot into an axillary bud. 



THE CANALS IN RETONOS. 



New shoots which take their origin from roots have this peculiarity 

 in common with the epicotyl, that they do not possess medullary canals 

 till several internodes have developed. They are further peculiar in lack- 

 ing primary cortical canals near their bases. A retono 23 mm. long was 

 examined and measured. A section near the root at the level of emerg- 

 ence showed neither pith nor cortical canals . At 5 mm . above it five cortical 

 canals were found. At 10 mm. there were three medullary canals, and at 

 1 5 mm. five of these, so that at the level of 1 5 mm. the definitive structure 

 had been attained. 



In another specimen 25 mm. long, collected September 8, 1908, only 

 one medullary was found at the level of 18 mm., and four at 21 mm. In 

 still another, one canal was found at 15 mm. 



An examination of a full series of transverse sections through suc- 

 ceeding nodes and internodes discovers an important relation of the pith- 

 canals to branches, in general harmony with the facts cited immediately 

 above. The material thus studied was a retono several centimeters long 

 which developed in 1908. The first leaf and its axillary bud were devel- 

 oped at the height of 20 mm. The internode between the mother-root and 

 this node had no pith-canal. At the first node a single canal appeared just 

 below the level of the bud, and entered this. The succeeding two inter- 

 nodes (second and third) were also devoid of canals, though at each of the 

 corresponding nodes a single canal originated in the pith and passed into 

 the axillary bud. At the third node, however, the canal branched, one 

 limb passing up into the fourth internode, in the upper part of which two 

 other canals appeared. One of these three sent a branch to the bud of the 

 fourth node, and one ended blindly, leaving two passing into the fifth 

 internode. At the fifth node one of these sent two branches into the bud, 

 two canals passing into the sixth internode. At the sixth node both of 

 these branched, one branch going into the bud and three upward into the 

 seventh internode. At the seventh node all three branched, one of these 

 going into the bud, leaving the full complement of five canals for the suc- 

 ceeding internode, the eighth. The youngest canal always stands opposite 

 the youngest bud. 



