182 Palaeontologie. — Eumycetes. 



led and beautifully illustrated memoir are summarized as follows: 

 The three British Coal-Measures, Heterayigium shorense, H. 

 tiliaeoides, and H. Lomaxii, agree in the more important charac- 

 ters and only differ in details. The further species, H. minimum, 

 is of a different type. The three species first named may conve- 

 niently be grouped in a provisional subgenus, Polyanghim, charac- 

 terized b\ T the leaf-trace, starting from the stele as two distinct 

 bundles, which further divide on their outward course, the number 

 of bundles in the petiole ranging from four to eight. In addition to 

 the polydesmic structure, these three species further agree iE the 

 sharp delimitation of the primary peripheral xylem-strands, with 

 the consequent differentiation and, large interfascicular principal 

 rays, and in the approach to exarchy in the peripheral Strands and 

 leaf trace bundles, the primary centrifugal xylem being comparati- 

 vely little developed. It is probable that, besides H. shorense, H. 

 tiliaeoides, and H. Lomaxii, the four species described by Renault, 

 from the Upper Coal Measures of Au tun (H. punctalum, H. Re- 

 naultii, H, Duchartrei and H. bibractense) are referable to the sub- 

 genus Polyangium. 



The Lower Carboniferous species H. Grievii may be taken as 

 the type of another. subgenus, Eu-heierangium , characterized by 

 the leaf-trace consisting of a Single bündle only, where it leaves 

 the stele, this bündle either remaining undivided on its outward 

 course or dividing into two Strands onl}\ One Dulesgate species, 

 H. minimum, falls under this subgenus, as do also four of the 

 Ostran species described b}' Dr. Kubart, namely H. alatum, H. 

 polystichum, H. Schusteri, and H. Sturii. The peripheral xylem- 

 strands are, on the whole, less distinct in Eu-heterangium than in 

 Polyangium, but the degree of their differentiation varies in the 

 different species. The x}Tem Strands may either be „centrally me- 

 sarch" or show a tendency towards exarchy. A third subgenus 

 may be required for the Lyginopteroid species, such as H. Andrei, 

 discovered by Dr. Kubart. 



The polydesmic species of Heterangiutn (Polyangium) show an 

 interesting analogy with Medulloseae and with the protostelic Cala- 

 mopityae. There is, however, no sufhcient evidence of any direct 

 phylogenetic relation to either group. With Rheiinangium there is 

 no special affinity, for, while the genus appears, to have much in 

 common with Heterangium, its leaf-trace is complex and not mul- 

 tiple, this presenting only a remote analogy with that of the poly- 

 desmic Heterangiums. Megaloxylon is altogether more remote. 



Agnes Arber (Cambridge). 



Coons, G. H., Factors involved in the Growth and the 

 Pycnidium Formation of Pleodomus fuscomaculans. (Journ. 

 agr. Res. V. p. 713—769. 1916.) 



Die Umgebungsfaktoren üben eine sehr starke Wirkung auf 

 das Leben des Pilzes. Er vermag sich wohl den verschiedensten 

 physikalischen Nährverhältnissen anzupassen, ist aber bezüglich der 

 Fortpflanzung anspruchsvoller. Pykniden bilden sich in der 

 Dunkelheit nicht. Haben sie sich aber in vollem Lichte gebildet, so 

 entwickeln sich die Fruchtkörper in der Dunkelheit weiter. Es 

 besteht also ein umgekehrtes Verhältnis zwischen Fortpflanzung 

 und Wachstum, da sehr helles L— 1 -" ~- r "'- " cklung 



des Myzels hemmend wirkt. Dir massig 



