GENERAL MORPHOLOGY 73 
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The leaves themselves were usually simple, as in LZywdsetum, though of 
greater dimensions, and accordingly more effective as assimilating organs ; 
but among the earliest forms, such as Asterocalamites (Schimper), from 
the Culm, the leaves were branched in repeated dichotomies (Fig. 199). 
In the very early Pseudobornia, from the upper Devonian of Bear Island,! 
the foliage was forked in a fan-like fashion, and of considerable dimensions. 
Another feature, in which certain of the earliest forms differed from the 
later, was in the fact that the members of successive whorls were super- 
posed, and did not alternate (e.g. Asterocalamites). Such forms have been 
Fic. 106. Fic. 197. 
Equisetum pratense, Ehrh. Shoots showing recurrent whorls Phyllotheca. Zigno. A, Ph. equisetiformis 
i from Rovere di Velo, near Verona. 48, inflores- 
of sporangiophores and of bracts. (After Milde.) 2 ¢ 
a Pee ; cence from Siberia, placed by Schmalhausen with 
Phyllotheca. (After Solms.) 
associated by Potonié as a family of “ Protocalamariaceae.” The facts 
would seem to indicate then a primitive construction of the Equisetoid 
shoot as having relatively large whorled and superposed leaves, effective 
as assimilating foliage: these were also separate from one another, and 
liable to bifurcation. The condition, as seen in the present Lgwzsefum, 
might be understood as attained by reduction of the coalescent and simple 
leaves, which became also alternate instead of superposed, while the 
assimilatory function was relegated almost entirely to the axis. But there 
is no certain proof that the actual evolution of Ayguzsetwm itself was along 
such a line as this. 
1Nathorst, Z.* Foss. Flora d. Folirlinder, i., Lief. 3, Tat 7.8 
