580 ALEXANDER W. EVANS 



of the species, at least, are separated by unsatisfactory and often inconstant 

 characters. This is particularly true of those drawn from the alar teeth and 

 from the female involucres. In the writer's experience the teeth, even on a 

 single thallus, may vary greatly in both size and shape, and yet differences no 

 greater than these variations have been utilized as differential characters. In 

 the case of the female involucres, where the lobes may be few and broad or 

 numerous and narrow, similar variations have been utilized. In all probability 

 the result of more intensive study would be the reduction of certain widely 

 recognized species to synonymy. 



Area of distribution: New Zealand; Australia; Tasmania; Chile; Juan 

 Fernandez; probably tropical America, 



Pallaviciiiia S. F. Gray. 



*22. P. xiphoides (Tayl.) Steph. Mem. Herb. Boissier 11; 314 (1900). — 

 Diplolaena xiphoides Tayl. Jour. Bot. 3: 569 (1844). — Fig. 6. 

 On soil. 



Masafuera: Q. del Mono, on the ground, 570 m. (no. 90); Q. de las Casas, 

 200 m. (no. 91, 92). 



The specimens from Q. del Mono agree in all essential respects with New 

 Zealand specimens of P. xiphoides in the Mitten Herbarium. Those from O. 

 de las Casas, however, tend to be more robust and to show a more gradual 

 thinning of the thallus in passing from the midrib to the unistratose portions 

 of the wings. At first sight these differences might appear to be specific in 

 character, and yet they might equally well come within the normal range of 

 variation of a single species. Since the specimens are completely sterile it 

 seems advisable to adopt the second view. 



An individual plant of P. xiphoides shows the usual differentiation into 

 a wingless rhizome and a winged thallus with a distinct midrib. The rhizome, 

 which is slightly flattened, is 0.18 — 0.35 mm. in width, and the surface may be 

 either smooth or more or less densely radiculose. Except at the very base the 

 rhizome is traversed by a slender strand of tracheid-like elements with brown 

 walls; the strand is about 30 [x in diameter and the individual cells about 5 [x. 

 On the outside an epidermal layer of thin-walled cells is present. The cells 

 average about 12 [j. in width, and their slightly bulging walls are usually more 

 or less tinged with brown. The rest of the rhizome is composed of from four 

 to seven layers of cells, averaging about 20 ij. in diameter and having thin, 

 colorless walls. The rhizome varies greatly in length; at one extreme it may 

 be scarcely i mm. long and at the other ma}' attain a length of 1.5 cm. It 

 gradually broadens out into the winged thallus, which soon curves or bends 

 upward and assumes an ascending position. 



The winged thallus is either free from rhizoids throughout or sparingly 

 radiculose in the basal portion The length may be as much as 3.5 cm. and 

 the width is i — 3 mm.; an individual thallus, however, rarely varies in width 

 to any great extent. The thalli sometimes branch once or even twice by 



