CYCADALES 163 



With the addition of histological characters the key devised by 

 Sister Mary Alice Lamb could be made sufficiently complete for 

 identification of the genera. In the large genera, she studied several 

 species. 



A key based upon the male gametophyte could probably be de- 

 vised. Some of the genera can be determined, at a glance, by the 

 cones. The two strong horns of Ceratozamia, the long spine of Ma- 

 crozamia, the elongated peltate top of Microcycas, the loose cone of 

 Dioon, and the crown of megasporophylls in Cycas provide an easy 

 identification. With all characters available, it is easy to make keys. 



For the convenience of students the following key, somewhat 

 modified from Pilger's key in Engler and Prantl, PHanzenf ami- 

 lien, may be as good as any: 



KEY TO THE GENERA OF CYCADACEAE 



A. Leaflets with a midrib, but no side veins. Mega- 

 sporophylls in a crown, through which the axis 

 continues to grow. Sporophylls with several 



ovules along the sides — Oriental i . Cycas 



B. Leaflets with a midrib and pinnate side veins. 

 Sporophylls, each with 2 ovules, forming a cone 



— Africa 2. Stangeria 



C. Leaflets parallel veined, no midrib. Megasporo- 

 phylls in cones, each with 2 ovules 



a) Leaflets bipinnate — Australia 3. Bowenia 



b) Leaflets once pinnate 



1 . Ovules on stalklike protrusions of the meg- 

 asporophyU and arranged in a loose cone — 



Mexico 4. Dioon 



2. Ovules sessile. Ovules with 



(a) shield-shaped top with two strong 



horns — Mexico 5. Ceratozamia 



(b) Sporophylls shield shaped, without 

 horns 



(i) Cones small; sporophylls in longi- 

 tudinal rows; leaves developed 

 singly, mostly small plants — 

 America 6. Zatnia 



(2) Cones large; leaves in crowns; 



mostly large plants — Africa 7. Encephalartos 



