ANATOMY AND AFFINITY OF CERTAIN RARE AND PRIMITIVE FERNS. 371 
which has been counted, and 72 the largest. 72 is probably the typical spore-number. 
This number is remarkably high for a genus showing an advanced “ mixed” condition 
of sporangia. The numbers recorded for such plants generally range between 48 and 
64. This has been shown by Professor Bower in his “ Studies in the Morphology of 
Spore-producing Members,” iv (Phil. Trans. Roy. Soc., 1899), and in The Origin of 
a Land Flora, and much smaller numbers are characteristic of some species of 
Nothochlaena, Cheilanthes, and Pellsea, and of Ceratopteris and Sadleria. Among 
Gradatse, 64 is the highest number yet recorded for Cyatheacese, Dennstsedtiinse , 
and Dicksoniese ; but in some species of Hymenophyllum and Trichomanes, and in 
the Simplices generally, the recorded spore-numbers exceed 128. A general survey 
of the Filicales shows that the transition from 64 to 128 is remarkably sudden. 
Accordingly, Jamesonia is of special interest as possessing a spore-output per 
sporangium ranging between these numbers. The high spore-output in Jamesonia 
may be considered a primitive character. Its recognition lends added interest to 
the irregularities of the annulus, and marks the genus as one in which the sporangial 
characters are not yet of fixed advanced type. 
General Conclusion. — It is not proposed to discuss here the value of the specific 
characters recognised by the systematists, for they refer chiefly to leaf-habit, and lead 
to the recognition of no features which aid in a question of generic affinity. Atten- 
tion may, however, be focussed on certain points in the foregoing survey of the 
structural features of J amesonia. 
The dermal appendages are of simple type, but throw no direct light on the 
phyletic position of Jamesonia, and display no special features which would justify 
detailed comparisons. The same may be said of the stele, for protostely, solenostely, 
and dictyostely may all exist within the limits of a single group. This is seen, for 
example, in the Schizseacese ; Lygodium, Sw., being protostelic, Aneimia mexicana, 
Kl., solenostelic, and Mohria, Sw., dictyostelic. But while the stelar state may not 
be decisive phyletically, the cortical characters may be used generically. The display 
of highly ventilated parenchyma immediately outside the stele is peculiar to J ame- 
sonia, and may be used as a subsidiary character in generic determinations. The 
undivided leaf-trace and the marginal pinna-trace supply are simple features, and 
while they may be matched from modern Schizseacese, they would not be decisive in 
a question of affinity. The structure of the pinnae and roots is expressive only of 
specialisation under xerophytic conditions. Thus though individually the structural 
features are indeterminate, collectively they constitute a relatively primitive 
anatomical state. 
The general “ Acrostichoid ” sporangial arrangement is open to alternative ex- 
planations. It may be a primitive arrangement comparable to that typical of 
modern Schizseacese, or the result of extension of non-indusiate sori along the veins. 
The sudden transition from the “ simple” to the “ mixed” condition during develop- 
ment of the superficially initiated sporangia is, however, a feature of advance. The 
TRANS. ROY. SOC. EDIN., VOL. LII, PART II (NO. 14). 58 
