1906] CURRENT LITERATURE 237 
connected with the study of algal ecology, and has suggested some means towards 
their solution. The first problem considered is the determination of what shall 
constitute a formation, and the contrast with terrestrial formations is made. 
Suggestions are made as to the significant unit and examples are given. Chief 
attention, however, is given to algal periodicity, the seasonal: variations of algae 
being much greater than those of terrestrial plants. ‘In most cases in an aquatic 
flora a number of dominant forms succeed one another in the course of a year, 
and after their period of prevalence is past they disappear either suddenly or 
gradually.” Periodicity of algae is either seasonal or irregular, and the factors 
concerned in both of these cases are discussed. In illustration of his statements, 
the author discusses the algal flora of a particular pond. e paper is a distinct 
stimulus to the study of pond life in an effective way,—]. M. ©. 
Decay of timber.—Following the lines of investigation laid down by Hartic 
in his Zersetzungserscheinungen des Holzes, BULLER?" has contributed a further 
study on the subject of the decay of timber caused by the higher fungi. The 
form studied is the common Polyporus squamosus, which is found on many 
Species of broad-leaved trees. Like other forms of this class, the fungus gains 
entrance to the tree through wound surfaces. The mycelium progresses more 
rapidly in a longitudinal direction in the wood, so that the decayed region extends 
many feet up and down the trunk and principal branches, while advancing only 
a few inches in a radial direction. The yphae penetrate into all the wood 
cells. The decaying wood is lighter in color than the sound wood. In the 
sound wood.—H. HassELBRrnc. 
Pogamy in Dasylirion.—Went and BLAAuw?”? have described apogamy in 
Dasylirion acrotrichum, in the case of plants in cultivation in the Utrecht Botan- 
teal Garden. This Mexican species is dioecious, and no staminate plants exist 
in the garden, thus precluding the possibility of fertilization. A certain number 
of fruits matured sufficiently to attract attention, and an examination of the 
development, in some cases completely filling the sac. Dasylirion is thus added 
to the very few illustrations of endosperm-formation without fertilization. In 
these endosperm-containing sacs no embryos were found, but in some others a 
8roup of cells was discovered in the usual position of the egg-apparatus, which 
the authors seem justified, judging from the figures, in regarding as a young 
embryo. The position would suggest a case of parthenogenesis, but there is room 
for doubt, and the authors prefer to speak of it as a case of apogamy.—J. M. C. 
Seth ica A. H. Recmatp, The biology of Polyporus squamosus. Huds., a 
oying fungus. Jour. Econ. Biol. 1: 101-138. pls. 5-9. 1906. 
ou —— F. E..F, - an Biaauw, A. H., A case of apogamy with Dasylirion 
m Zucc. Recueil Tray. Bot. Néerland. no. 3. pp. 12. pls. 5. 1905. 
