144 ILLINOIS ACADEMY OF SCIENCE. 



STRUCTURE OF THE ADULT CYCAD STEM. 



By Charles J. Chamberlain 



University of Chicago. 



(Summary.*) 



1. The paper deals with field material of adult stems of Dioon 

 spinulosum, D. edule, Ceratozamia mexicana, and Zamia flori- 

 dana, particular attention being given to Dioon spinulosum. 



2. In Dioon spinulosum the xylem zone in a plant 6 meters in 

 height reaches a width of 10 cm., far exceeding the extent of any 

 xylem zone previously described for any cycad. 



3. Dioon spinulosum and D. cdule have growth rings, which in 

 D. spinulosum correspond to the periods of activity which result 

 in the formation of crowns or cones, but which in D. edule do 

 not correspond to such periods. No growth rings were found 

 in Ceratozamia mexicana or Zamia floridana. 



4. Cone domes in the pith were studied in the four species. 



5. The histological character of the adult stem was studied in 

 Dioon spinulosum. The protoxylem consists of scalariform 

 tracheids, from which there is a gradual transition to the trach- 

 eids with mtultiseriate bordered pits, constituting the principal 

 part of the wood. There are also cells with the same origin as 

 the pitted tracheids, but with transverse walls which may remain 

 thin-walled and contain starch or may become lignified. Besides 

 the leaf trace bundles, scalariform tracheids are found in the 

 large medulary rays. 



6. Both in the general appearance of the transverse section 

 and in histological characters the adult trunk of Dioon spinulo- 

 sum resembles that of Cycadeoidea. 



Discussion. 



Mr. Coulter. — "It is a matter of considerable interest, if I 

 might emphasize, to discover in Mexico a Cycad which has con- 

 tradicted one of the best established distinctions of the Cycads 

 as distinct from the Conifers, and it suggests a possibility that no 

 one had thought of before. It is an absolutely new thing among 

 Cycads to have such massive wood, and wood of this kind." 



Mr. Caldwell. — "Just what is the connection between that 

 hump of wood that bears the cone, and the cylinder rings?" 



*Published in full in the Botanical Gazette, under the title "The Adult Cycad 

 Trunk," 52: 81-104, Aug., 1911. 



