Form of H or midium fiaccidum , A. Braun. 517 
in detail below. Highly refractive granules and rounded masses generally 
accumulate in the cells (cf. p. 525), but the abundance and size of these 
depend on the food reserves available on the advent of drought, as well as 
on the degree of desiccation. Abundant starch is usually associated with 
the granules when numerous. Another effect of prolonged drought is the 
frequent contraction of the chloroplast away from the cell wall, the proto- 
plasm remaining in contact with the latter ; the chloroplast also tends to 
become a yellowish green. When the temperature is high, the outer layer 
of the cell wall, the ‘ cuticle Y cracks, and may become detached in small 
pieces. 
In nature, Hor midium flaccidum may become infected by a parasite. 
This has not so far appeared in the Woodford Alga, but was found daring 
the summer of 1915 in a form growing at Loughton, Epping Forest. 
Certain, usually scattered, cells were then observed to be filled with numerous 
minute ovoid organisms, which were perfectly colourless ; the contents of 
the cells in question had either completely disappeared or become reduced 
to a thin peripheral vesicle often green in colour (Fig. 2, b). The cells of 
the parasite were frequently swarming, and would eventually escape through 
an aperture in the longitudinal wall (Fig. 2, C). They could subsequently 
be seen rotating about their longitudinal axis and swimming through the 
surrounding water. The organism is probably one of the Chytridiaceae, 
several of which are known to occur in the filaments of Ulotrichales. 1 2 
* 3. Splitting. 
The splitting of the filaments at the transverse walls was recorded in 
Hormidium by A. Braun, 3 and has subsequently been examined in 
II. dissectum ( Ulothrix dissecta) by Gay, 4 in II. nitens by Klebs, 5 and in H. 
flaccidum by Gay, 6 Klebs, 7 and Borzi. 8 
In H. dissectum Gay observed the middle lamella of the septum to 
dissociate from the periphery inwards, fission resulting. The separation 
proceeded in an unsymmetrical manner, being more marked at one side of 
the filament than at the other, so that the two resulting fragments were 
inclined to each other. According to Gay, H. dissectum dissociates actively 
1 This term, already adopted by Klebs and others, merely denotes the distinct, thin, external 
layer of the longitudinal wall. It has none of the characteristic properties of ordinary cuticle. 
2 Cf. Lemmermann : Die parasitischen u. saprophytischen Pilze der Algen. Abh. Nat. Ver. 
Bremen, xvii, 1901, p. 185 etseq. 
3 A. Braun : Rejuvenescence in Nature, Leipzig, 1851. English translation by A. Henfrey, 
p. 1 31, foot-note. 
4 F. Gay : Recherches sur le D^veloppement et la classification de quelques Algues vertes. 
These, Paris, 1891, p. 60. * 
5 G. Klebs : Bedingungen der Fortpflanzung, Jena, 1896, p. 329 et Seq. 
1. c., p. 63. M.c., p.341. 
8 Borzi : Studi algologici, fasc. ii, 1895, pp. 361-9, 
