CYCADALES 



99 



zone is usually only one cell wide, the cells are so enlarged radially 

 that the zone is easily visible to the naked eye. These roots are al- 

 most universal in seedlings and are 

 much more prevalent in the green- 

 house than in the field. 



THE SPOROPHYTE — REPRODUCTIVE 



No plants are more absolutely 

 dioecious than the cycads (fig. 93). 

 Schuster reports one case in Cycas 

 revolida where a plant was cut into 

 two longitudinal pieces, which were 

 taken to difi"erent places. It is claimed 

 that one piece produced a female 

 strobilus and the other, a male. On a 

 lawn in Australia there were several 

 plants of Cycas revoluta. It was re- 

 ported to me that one of these pro- 

 duced a female strobilus and, a few 

 years later, a male strobilus. It is 

 also claimed that a bud from a fe- 

 male plant of Cycas circinalis, in the 

 Garfield Park Conservatory at Chi- 

 cago, reached the coning stage and 

 produced a male cone. In 30 years 

 of study in the field and in green- 

 houses I have never seen anything 

 to indicate that the cycads are not 

 absolutely dioecious. 



It will be remembered that in the 

 Bennettitales the strobili are pre- 

 vailingly bisporangiate. The reduc- 

 tion from the bisporangiate condi- 

 tion to the dioecious is a general 

 tendency in plants. 



The female strobilus *— The largest cones that have ever existed 



* The term "strobilus" is used to include both the crowns of loose sporophylls, like 

 the female sporophylls of Cycas and the male sporophylls of Cycadeoidea, and compact 



Fig. 91. — Cycas revoluta: coralloid 

 masses of root tubercles on erect 

 (apogeotropic) roots. — From Cham- 

 berlain, The Living Cycads"" (Uni- 

 versity of Chicago Press). 



