Physiologie. — Algae. 325 



nen, also mit dem geringsten Kraftaufwand, zu transportieren und 

 danach regelt sich das Dickenwachstum der Stämme. 



Im Herbst, bei der stark verringerten Assimilaiionsarbeit der 

 Blätter, erfolgt das Dickenwachstum wahrscheinlich vornemlich auf 

 Kosten der Reservestoffe. Bei plötzlich gestörtem Gleichgewicht 

 zwischen den Verdunstungsorganen und den jüngsten Leitungsge- 

 weben treten auch die letztjährigen subperipherischen Jahrringe 

 wieder in den Dienst der erhöhten Wasserzirkulation. 



H. Detmann. 



Fritsch, F. E., The Morphology and Ecology of an Ex- 

 treme Terrestrial Form of Zygnema {Zygogoiiiutn) ericetorum 

 (Kuetz.) Hansg. (Annais of Botany. XXX. 117. p. 135—149. figs. 

 january 1916.) 



This alga owes its peculiarities to its very inhospitable habit 

 on Hindhead Common. The mature cell contains two chloro- 

 plasts. After cell-division the daughter cells contain a Single chloro- 

 plast for a time. Division is performed by a gradual infolding of 

 the innermost layer of the cell- wall, but is left incomplete for a 

 time, the daughter-protoplasts being still connected through a cen- 

 tral pore. Two or three layers are distinguishable in the longitudi- 

 nal wall. The Hindhead plant remains permanentl}^ in the akinete 

 condition. The outer portion of the w^all is strongly thickened and 

 mucilagenous, and plays a great part in protecting the cells during 

 drought and in promoting a rapid recovery afterwards. At the be- 

 ginning of a drought the fat-globules in the cell move to the peri- 

 phery and form a very dense layer upon the inner face of the 

 cell-walls. Some hours after the moistening of the dry plant the 

 fat-globules have become dispersed again. At the beginning of a 

 drought the protoplasts round off slightly and develop a new layer 

 of membrane. Each cell divides at the most but twice between two 

 successive periods of drought. Another method of akinete formation 

 has been noticed early in the year; there is an unequal cell division, 

 resulting in the formation of an akinete and of a much smaller 

 pigment-cell. The contents of the pigment-cells subsequently disap- 

 pear, and the empty cells form weak points, where the filament 

 readily ruptures. E. S. Gepp. 



Fritsch, F. E. and H. Takeda. OnaSpeciesof Chlamydomonas 

 (C. sphagnicola F. E. Fritsch and Takeda — Isococcus sphagni- 

 colus F. E. Fritsch). (Annais of Botany. XXX. 119. p. 373—377. 

 July 1916.) 



The authors are of opinion that this green flagellate alga does 

 not constitute a distinct genus, but is a somewhat peculiar species 

 of Chlamydomonas. It was found at Keston (Kent) and in Rich- 

 mond Park. It is rather large, more or less ellipsoid, with very 

 thick cell-wall (outer layer firm, inner layer gelatinous and four 

 times as thick), having at the anterior pole two papillae, or a Single 

 Papilla which is usually bilobed — one of the most striking features 

 of the plant, The flagella are about one quarter longer than the 

 cell; chromatophore Single; pyrenoids four or more, and conspi- 

 cuous; Stigma conspicuous; nucleus central; contractile vacuoles 

 two; propagation by longitudinal division of the mother-cell into 

 two, four or eight parts. E. S. Gepp. 



