Boodle.—Anatomy of the Hymenophyllaceae. 465 
One may summarize the structural characters of the stele 
thus :■— 
1. The phloem forms a ring round the xylem. 
2. In species with large rhizomes the metaxylem forms a 
ring enclosing parenchyma and protoxylem ; the metaxylem 
often has the form of two bands. 
3. In species with small rhizomes the metaxylem forms 
a small band or mass, and the protoxylem is peripheral to it 
on the lower side. 
4. Signs of transition between % and 3 occur. 
Hymenophyllum, roots. 
In Hymenophyllum the roots are described as being mostly 
diarch. H. demissum } var. nitens, may be mentioned as having 
a typical diarch root, while the root-stele of H. dilatatum^ var. 
Fosterianum , is much smaller, and appears to be monarch ; 
the root*stele of H. scabrum in passing through the cortex of 
the rhizome also appears to be monarch. In this genus and 
in Trichomanes the root structure does not appear to be of 
any great interest, apart from the fact that the number of 
protoxylem-groups differs according to the stoutness of the 
stele 3 . The higher numbers of protoxylems are found only 
in Trichomanes. The largest number found by Russow 2 was 
eight, and by Prantl 3 nine. Russow 4 thought that diarch roots 
were restricted to Hymenophyllum , monarch and triarch up to 
octarch roots being found in Trichomanes , but Prantl 5 found 
that this rule did not hold good. Where monarch roots occur 
in the Hymenophyllaceae they are probably so by reduction, 
because the primary root of Trichomanes alatum is diarch, as 
proved by Leclerc du Sablon 6 . 
1 Prantl, 1 . c., p. 31. 
2 Russow, Vergleich. Unters. d. Leitbiindel-Krypt., Mem. de PA cad. Imp. d 
St. Petersb., VII, 19, 1872, p. 95. 
3 Prantl, 1 . c., p. 31. 
4 Russow, 1 . c., p. 95, note. 
5 Prantl, 1 . c., p. 31. 
9 Leclerc du Sablon, Ann. des Sci. Nat., 7® ser., t. xi, p. t i. 
