An exchange of views on the Cyatheaceae

When Dr. R.E. Holttum kindly submitted the following essay review of two papers on Cyatheaceae, a suggestion that Dr. R.M. Tryon be enabled to reply was welcomed by both pteridologists. The editor feels grateful to them for their contribution. First Dr. R.E. Holttum: GASTONY, G.J. Spore morphology in the Cyatheaceae. I. The perine and sporangial capacity: General considerations. Amer. J. Bot. 61 (1974) 672-680. GASTONY, G.J. & R.M. TRYON. Ibid. II. The genera Lophosoria, Metaxyas Sphaeropteris, Alsophila and Nephelea. Amer. J. Bot. 63 (1976) 735-758.