Sellards — Fronds of Crossotheca and Myriotheca. 201 



on both micro- and megaspores of Selaginella, and the Car- 

 boniferous Lycopods, as well as on such heterosporous living 

 ferns as Marsileci. The tetrahedral division of the spore mother 

 cell, of which the three radiating lines are indicative, is well 

 known to be extremely constant, not only for the Pterido- 

 phytes, but for all those plants commonly grouped under the 

 Archegoniatese, and for the microspores of most of the flower- 

 ing plants.* 



The lines, therefore, cannot be considered characteristic of, 

 or in any way distinguishing megaspores. Their absence in 

 some cases may be due to imperfect preservation, or they may 

 be obscured by the view of the spore presented. In the case 

 of P arlierioidea^ there is some doubt as to whether it is not 

 possible that the spores when seen from the apex present the 

 lines and a smooth face, and when seen from the base are sculp- 

 tured, the lines being obscured by the thickness of the spore. 



The recent studies of Prof. Bowerf have directed attention 

 to the importance of the size of the spores and the number to 

 the sporangium. Bower's investigations show that among liv- 

 ing ferns an increase in the size of the spores, correlated with 

 a decrease in the output to the sporangium, accompanies, in a 

 general way, the advance in development and specialization 

 from the Marattiacese through the various families of the 

 Leptosporangiate ferns. The little that is definitely known of 

 the spores of fossil ferns supports Bower's conclusions. It is a 

 question, however, how far the size and number of the spores 

 may be relied upon to separate Marattiaceous from non-Marat- 

 tiaceous ferns. 



The spores of Pecopteris villosa are smaller than those of 

 such living Marattiacese as Angiopteris evecta, Kaidfussia^ 

 Marattia Douglassii^ or Danceci moritziana. Crossotheca and 

 Myriotheca have much larger spores, comparable in size to 

 many of the Leptosporangiate ferns. It is hardly possible, 

 with fossil ferns, to count the number of spores to the spo- 

 rangium, but it is evident that in the case of Pecopteris unita 

 and P, villosa^ the output to the sporangium was very great, 

 while that of Crossotheca and Myriotheca was comparatively 

 small. 



Geological Department, Yale University Museum. 



* See Campbell, University Text-book of Botany, 1902, pp. 199 and 323. 



f Studies in the Morphology of Spore-Producing Members, Parts III and 

 IV, Phil. Trans. Eov. Soc, vol. clxxxix, 1897, pp. 35-81 ; vol. cxcii, 1899, 

 pp. 29-138. 



