72 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Peculiar Unattached Mode of Growth of Leucobryum.* — W. H. 

 Burrell describes the common but insufficiently known occurrence of 

 Leucobryum glaucum in the form of unattached flattened balls, measuring 

 1-2 inches in diameter. They are found with normal attached tufts 

 under beech-trees, where they tend to be kicked about by game-birds 

 and other animals that feed upon beech-nuts. The thick spongy water- 

 retaining nature of the leaves, and the free formation of adventitious 

 buds, are other factors that contribute to the production of the cushions, 

 as the plants contain a sufficiency of water for prolonged independent 

 growth, and the numerous buds swelling out tend to produce a ball of 

 branches radiating from near a common centre. The author cites a 

 description by H. N. Dixon of unattached balls of Porotrichum 

 alopecurum in moist hollows in Weldon Quarries in Northamptonshire. 

 These balls measure 2-5 inches in diameter, and consist of profusely 

 branched stems. 



Thallophyta. 



Algse. 



By Mbs. E. S. Gepp. 



Regeneration of Algse.f — S. Prowazek has been studying the 

 subject of regeneration of algae at intervals for the last six years, and he 

 now publishes the most important of his results. His investigations 

 were made on the following species : Spirogyra Weberi Kiitz., Mougeotia 

 gemtfiexa Ag., Ulva lactuca, Cladophora, Bryopsis plumosa, Vaucheria 

 sessilis, Valonia, and Ectocarpus. His results are described under the 

 following headings : 1. Phenomena which arise during or immediately 

 after infliction of the wound (irritation and wounding phenomena). 



2. Regeneration and reparation phenomena in the narrow sense. 



3. Regeneration phenomena which exceed the original limit of form- 

 structure. The paper is illustrated by text figures. 



Influence of External Conditions on the Asexual Reproduction 

 of Algas.J — H. Freund describes the experiments which he has made 

 on this subject, with the results at which he has arrived. Among some 

 of the conditions with which he experimented are temperature, intensity 

 of light, increase and removal of nutritive salts, etc. The first plant 

 dealt with is (Edogonium pluviale, and after detailing many series of 

 experiments, he gives an interesting comparison between (E. pluviale, 

 (E. diplandrum, and (E. capillar e. Hccmatococcus pluvialis was also 

 treated. A section devoted to general considerations is followed by a 

 summary of the results of this work. 



In CE. pluviale and H. pluvialis, the external conditions necessary 

 to the formation of zoospores differ according to the previous conditions 

 of growth. The significance of inorganic salts for the formation of 

 zoospores in both algas depends in the first place upon their chemical 

 properties. After treatment with Knop 1 s nutritive solution, (E. pluviale 

 forms zoospores, if nitrate and phosphate have been withheld. Diminu- 



* Bryologist, x. (1907) pp. 108-11 (figs.). 



t Biol. Centralbl., xxvii. (1907) pp. 737-47 (11 figs, in text). 



% Flora, xcviii. (1907) pp. 41-100. 



