330 Vegetation of Drying Mud and Retarded Germination. 



of West (Algae. Camb. Bot. Handbook, 1916, p. 416), that 

 ' It seems highly probable that some form of resting spore of 

 Botrydiiim, probably a hypnocyst, is universally distributed 

 in the mud of freshwaters in temperate regions, and also in 

 many parts of the Tropics, since the vegetative plants almost 

 invariably appear when such mud attains a certain degree 

 of dryness.' (The water content of mud bearing Botrydium 

 examined by the writer varied between 68-4% and 74% of 

 the dry weight.) 



The next phase marks the advent of Phanerogamic seedlings, 

 and occasionally of Riccia crystallina. It will be recalled 

 that Stahl found Oedocladium protonema [Pringsh. Jahrh. 

 f. wiss. Bot., XXXIII., 1891) on damp mud, and Oedocladium 

 albemarlense was found by Lewis in the same type of habitat 

 ('Tuffs. Coll. Stud., pp. 71-72, 1918). That such rare algae 

 occur here, as well as rare Phanerogams (c.f., below), is a 

 point of interest, but the fact of chief importance is that both 

 the American and Continental species of this genus were 

 found associated with Riccia, Vaucheria and Botrydium. It 

 is therefore not unreasonable to hope that Oedocladium may 

 yet be found in Britain. 



Although the three genera just mentioned mark separate 

 phases in the succession, when they occur as dominants, it 

 is, of course, not unusual to find them intermingled. 



As regards the Phanerogamic successors to the cryptogamic 

 pioneers, the appended lists show that there is considerable 

 variation, but the outstanding feature is the presence in great 

 abundance of species normally regarded as rare or even very 

 rare. These are for the most part annuals, and consequently 

 dependent upon favourable conditions for germination in 

 order to colonise the mud. Among the more noteworthy of 

 these may be cited Limosella aquatica, Riimex limosiis and 

 Alopecurus fulvus. The last named is stated in the Floras to 

 be a perennial, on what authority I have been unable to 

 ascertain. Its erratic occurrence does not harmonize with 

 this view, and Watson, who grew the species for six years in 

 his garden, definitely states that it behaved as an annual, 

 though, obsessed by the current belief, he adds, ' perhaps 

 because growing on dry ground ' (C. C. Watson, Top. Bot., 

 Vol. III., p. 162). Whilst it would be rash to deny that 

 A. fulvus ever behaves as a perennial, it is certainly often, if 

 not invariably, annual in its natural habitat. Both at Tring 

 and Elstree this species was found in some plenty on the 

 drying mud. Though apparently not there in the years 

 immediately proceeding, it was found growing plentifully by 

 Coleman prior to 1863. It has been similarly recorded as 

 abundant at Ruislip Reservoir, though unknown there previous 

 to its appearance in quantity. 



Naturalist 



