246 Algae. — Eumycetes. 



Piercy, A., The Structure and Mode ofLife of a Form of 

 Hormidium flaccidum A Braun. (Ann. of Bot. XXXI. p. 513 — 537. 

 3 Tab. and 6 text figs. London 1917.) 



The author gives a general account of the life of a form of 

 Hormidium flaccidum A. Braun in its native habitat. The survival 

 of the vegetative filaments throughout successive seasons of the 

 year is described, and their modification during drought, chiefly in 

 the accumulation of refractive granules, ancl in changes of the lon- 

 gitudinal walls and septa. A detailed deseription is given of the 

 two common methods of reproduction, viz.: 1) transverse Splitting 

 of the filaments at the septa, and 2) production of aplanospores. 

 Regarding 1), a general breaking up of the filaments into isolated 

 cells or few-celled pieces has not been observed; the Splitting oc- 

 curs at somewhat distant points in a filament, though in favourable 

 circumstances a minor proportion of the filaments have become 

 divided into few-celled fragments. It is suggested that Splitting is 

 due to the effects of renewed turgor on desiccated filaments in which 

 degeneration of the cuticle or a weakening, due to the development 

 of mucilage between the two lamellae of the septa, has taken place. 

 2) The production of aplanospores occurs in all reasons of the year, 

 but is dependent on an ample supply of water. Cells that give 

 rise to aplanospores usually contain an abundance of a special 

 substance and also granules. A white refractive substance is de- 

 scribed; it appears in the cells under certain conditions in the 

 form of granules and rounded masses. It arises chiefly in the re- 

 gion of the polar vacuoles, but also sparsely distributed in the pe- 

 ripheral protoplasm. Two conditions favour its production, viz. 

 drought, and a plentiful supply of carbohydrates, e. g. glucose. It 

 appears to be associated with a second special substance (referred 

 to above), and possibry is formed as a result of concentration of 

 this substance. Since, in suitable circumstances, the cells are ca- 

 pable of eventually absorbing the granules, these evidently serve 

 as a food-store. During the first weeks of a period of drought the 

 death-rate decreases, while the abundance of granules increases to 

 a maximum. When growing in its native, this alga in all proba- 

 bility rarely passes beyond this first stage of desiccation, as the 

 spelis of dry weather in temperate regions are comparatively short, 

 and dew is continually deposited, especially in summer when the 

 drought is most extreme. E. S. Gepp. 



Klebahn, H., Ueber Spezialisierung und spezialisierte 

 Formen im Bereich der Pilz. (Die Naturwissenschaften. V. 

 p. 543—550. 1917.) 



Eine kurze Uebersicht über die Erscheinungen der Heteroecie 

 und der Spezialisierung insbesondere der Rostpilze. Von allgemei- 

 nerem Interesse sind die Betrachtungen über das Zustandekommen 

 der Spezialisierung. In vielen Fällen dürfte die Gewöhnung an be- 

 stimmte Wirtpflanzen die Ursache sein. Diese Theorie setzt die 

 Pleophagie des Pilzes als den der Spezialisierung vorausgehenden 

 Zustand voraus. Zweifellos gibt es aber Fälle in welchen die Pleo- 

 phagie nicht der primäre sondern der abgeleitete Zustand ist (z. B. 

 bei Cvonartium asclepiadeum). Diese neuerworbene Pleophagie kann 

 sprungweise zu Stande kommen {Cron. asclepiadeum auf Schisan- 

 thus und Tropaeolum) oder durch Vermittlung einer dritten Wirt- 



