The Structure and Mode of Life of a Form of 
Hormidium flaccidum, A . Braun . 1 
BY 
ALMA PIERCY, M.Sc. 
With three Tables and six Figures in the Text 
i. Introductory. 
I N recent years a considerable amount of work has been published on the 
development and reproduction of Green Algae, but little attention has 
been paid as a rule to the way in which they vary in response to changes in 
the external conditions. Fritsch and Rich , 2 among others, refer to a special 
* winter form ’ of Cladophora , produced by the cells of the ordinary filaments 
thickening their Walls, darkening in colour, and accumulating abundant 
starch, besides often assuming an irregular, inflated shape. Few other 
data are to be found in the literature. It is to be supposed that terrestrial 
Algae, often exposed to extreme climatic changes, which they have frequently 
been noted to endure very successfully, should quickly and definitely 
respond to alterations in external conditions. 
Oltmanns , 3 however, does not cite any records of special adaptation to 
drought occurring in such terrestrial Algae as Pleurococeus, Hormidium , and 
Chlorella. Nor does the recent summary by Petersen 4 of experiments on 
the power of various terrestrial Algae to withstand prolonged drought shed 
any light on the possible response of the Algae concerned to desiccation. 
On the other hand, Fritsch 5 has recently observed various effects of drought 
in Zygnema ericetorum , notably the special peripheral disposition of its ‘ fat * 
globules. With a view to throwing further light on the adaptation of 
1 From the Botanical Laboratory, East London College, University of London. 
2 F. E. Fritsch and F. Rich : Biology and Ecology of the Algal Flora of Abbot’s Pool, near 
Bristol. Bristol Naturalists’ Society’s Proceedings, Fourth Series, vol. ii, part ii, 1909, p. 40; and 
J. Comere : Observations sur la Periodicite du developpement de Ja flore algologique dans la region 
toulousaine. . Bull. Soc. Bot. de France, t. liii, 1906, p. 399. 
3 Oltmanns: Morphologie u. Biologic d. Algen, vol. ii, 1905, p. 352. 
4 J. B. Petersen: Studier over Danske aerofile Alger. Mem. Ac. Roy. d. Sc. et d. Lettres d. 
Danemark, 7 e ser., t. xii, 1915, p. 353. 
6 F. E. Fritsch: The Morphology and Ecology of an Extreme Terrestrial Form of Zygnema 
( Zygogonium ) ericetorum (Kuetz.), Hansg. Ann. Bot., vol. xxx, 1916, p. 143 et seq. 
[Annals of Botany, Vol. XXXI. Nos. CXXXII and CXXIV. July and October, 1917,] 
