476 BOTANICAL GAZETTE [JUNE 
internal endodermis in this family have not “‘intruded” through branch gaps. 
The general conclusion is that the stele of the existing Osmundaceae is a “reduced 
amphiphloic siphonostele,” and that it is consistent with JEFFREY’s theory of the 
origin of the siphonostele and the homology of the pith—J. M. C. 
Morphology of Laminaria.—A knowledge of the reproduction of Laminaria 
has long been a desideratum, and this has now been supplied to some extent by 
Drew,** who has succeeded in making cultures according to methods he describes. 
He has concluded that the ‘‘sporangia”’ described as imbedded in the reproductive 
areas are in reality gametangia. These gametangia produce gametes (heretofore 
thought to be zoospores) which conjugate and produce zygospores. The zygo- 
spores give rise to a chain or mass of cells which may represent the 2” generation; 
and this in turn gives rise to the Laminaria plant, which represents the x genera- 
tion. The x and 2x conditions are inferences, as no cytological work was done; 
and the direct outgrowth of the young Laminaria plants from the “chain or mass 
of cells” would hardly suggest an intervening reduction division. However, the 
discovery that the reproductive areas consist of gametangia and paraphyses is of 
sufficient interest. The gametes when liberated seem to have no cilia, but soon 
develop them. The cells of the structure (chain or mass) produced by the 
zygospore “rupture, and their contents grow out to form the gametophyte.” 
Details are ‘ee of the development of the various regions and tissues of the young 
plant.—J. M 
The ecology of Zostera.—OsTENFELD has given an interesting ecological 
account of Zostera marina, as seen in Denmark.35 The structure and growth of 
the plant is first treated in detail, following which is an account of the necessary 
life conditions of the plant and the variations in diverse habitats. While Zostera 
requires salinity, it thrives where the percentage of salt is high (3.3 per cent), and 
also where it is very low (0.6 per cent). It occurs only in relatively quiet waters, 
and grows at greater depths in clear than in muddy waters, sometimes living at as 
great a depth as 11™ where the water is very transparent. The most important 
factor in determining its luxuriance appears to’be the character of the bottom, 
plants on firm sand having short narrow leaves, whereas plants in mud have 
long broad leaves (sometimes more than 2™ in length). A detailed account of the 
distribution of Zostera in Danish waters is followed by a discussion of the Zostera 
vegetation as a habitat; many plants and animals live where a Zostera vegetation 
has become established, the plants themselves often being covered with many 
forms. Other flowering plants that grow with Zostera are briefly described.— 
H. C. Cowes. 
34 Drew, G. Haroip, The reproduction and early development of Laminaria 
digitata and Laminaria dacoberiae, Annals of Botany 24:177-190. pls. 14, 15. 197° 
35 OSTENFELD, C. H., On the ecology and distribution of the grass-wrack (Zostera 
mar sees in eres wate: From Report Danish Biological Station. pp. 62- Sigs. 9- 
Copenha, 
