HIS WRITINGS 147 



about 1 2 10, embracing 1267 species, of which about 250 appeared 

 under the joint authorship of Dr Greville and himself. These 

 figures are in themselves sufficient evidence of the extent of his 

 Pteridographic work. 



It has been noted that the number of genera in the Genera 

 Filicum was 135, maintained approximately according to the 

 limitations of Presl in his Tentamen Pteridographiae : allowance 

 has, however, to be made for 23 genera of Parkeriaceae, Schi- 

 zaeaceae, Osmundaceae, Marattiaceae, Ophioglossaceae, and 

 Lycopodiaceae, which were omitted in the Tentamen. But in the 

 Synopsis Filicum there were only 75. It is true that the three 

 genera of Lycopodiaceae were excluded also from the Synopsis^ 

 but still there is the wide discrepancy between 132 of Presl's 

 genera as against 75 in Hooker's Synopsis. This at once indi- 

 cates a salient feature of his method. He merged a large 

 number of genera, ranking many of the smaller ones as sub- 

 genera under the more comprehensive headings. Doubtless 

 the reasons for this were various. One was his mistrust of ana- 

 tomical data, which it must be confessed Presl put too much in 

 the fore-front. The very first sentence of the Tentamen runs 

 thus "Vasa plantarum principale signum esse ex eo patet, quod 

 exinde primaria divisio omnium plantarum exstitit." But occa- 

 sionally Sir William explained his reason in a specific case. Thus 

 in the question of Kunze's sub-genus Plagiogyria of the genus 

 Lomaria, which Mettenius had raised to the dignity of a distinct 

 genus, he explained his reasons for merging it into the genus 

 Lomaria. Mettenius had laid stress upon various characters, but 

 especially on the oblique annulus as distinctive. On this Hooker 

 remarks " even should the capsules in all the species referred to 

 Plagiogyria prove to be helicogyrate, yet the habit and sori are 

 so entirely in accordance with true Lomaria that, unless the 

 student has the opportunity of examining very perfect speci- 

 mens, or unless he examines the structure of the annulus of the 

 very minute capsules under the high power of the microscope, 

 the genus cannot be identified. Kunze only proposed to form 

 a group or section under the name of Plagiogyria, but even that 

 would be found inconvenient to retain in a work whose main 

 object is to assist the tyro in the verification of genera and 



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