Boodle.—Anatomy of the Hymenophyllaceae. 493 
Thomae describes the petiolar bundle of H. tunbridgense 
correctly. Two of Giesenhagen’s papers have been referred 
to above. In the earlier paper 1 he puts forward the view 
that the function of the vascular bundles in the smaller mem¬ 
bers of the Hymenophyllaceae is not for the supply of water 
to the assimilating tissue, but partly, at any rate, for the 
receptacle. In Van Tieghem’s Traite 2 , the stems of Tricho- 
manes and Hymenophyllum are given as examples of the 
occurrence together of centripetal and centrifugal wood, 
the centripetal wood beginning towards the middle of the 
radius, and possessing centrifugal wood outside it. This 
description would not apply to any sub-collateral types nor 
to T. scandens. It would serve for species with more than 
one protoxylem-group embedded in the metaxylem, but, if 
one regards the region of the stem of H. scabrum , where there 
is only one protoxylem, it would not hold good. There is 
in this case no centripetal wood ; the first-formed among the 
protoxylem-elements are central to the others. Poirault 3 
makes a comparison of the structure in the young stem of 
Trichomanes with that of the node of Gleichenia. He refers 
to the researches of Leclerc du Sablon on the young plant 
of T. alatum , and it is not quite evident from his description 
whether his data are taken entirely from Leclerc du Sablon’s 
work, or whether he has made a further investigation of 
Trichomanes himself. If the former, he appears to have 
confused Leclerc du Sablon’s description of T. alatum with 
that of an entirely different type. Leclerc du Sablon makes 
no mention of the appearance of sieve-tubes within a pith 
in T. alatum , and it is on this point that the comparison 
is founded. The presence of internal sieve-tubes certainly 
seems very improbable. 
1 Giesenhagen, Die Hymenophyllaceen, Flora, 1890, p. 447. 
2 Van Tieghem, Traite de Botaniqne, second edition, 1891, p. 763. 
3 Poirault, Recherches sur les Cryp. Vase., Ann. des Sci. Nat., 7 0 ser., t. xviii, 
i 893 > P- 177 - 
