— 97 — 



tely during a pari of the year, re-appearance diépends largeh (in 

 some cases perhaps entirely) on germination of the resting spores 

 (cf. also Oedogonium). The problem thus arises whether Uie 

 absence of the necessary t'aetor in a sufïicient degreeof intensity 

 prevents the germination of the resting spores, or whether such 

 germination nevertheless takes place, but the unfavonrable con- 

 ditions do not admit of any marked growth of theyoung plants. 

 We hère corne lo the difficult question of decitling how far 

 inhérent tendencv plays a part in determining the periodicity of 

 Algae c1) . The matter can scarcely be completely solved without 

 the aid of experiments. We think liowever that inhérent ten- 

 dencv can only come into play in the case of the germina- 

 tion of resting spores. On the other hand the complète absence 

 of Spirogyras in Abbot's Pool (Fritsch and Kicli, 1909, p. 38) 

 under unfavourable conditions rat lier speaks against inhérent 

 tendency in tins case at least. The matter will be further discuss- 

 ed in the next section. 



We hâve frequently found in the preceding considérations 

 that a given form exhibits a far more prolonged maximum in 

 certain years than in others, although in some cases tins long 

 maximum leads to a persistence during months in which the 

 conditions were apparently not at ail suitable for the form in 

 question Thèse seeming anomalies are we think to be explained 

 as the resuit of impulse owing to exceptionally favourable con- 

 ditions at the time of initiation of the maximum. In illustration 

 of this feature, the following cases are worthyof considération : 



I. — The long-continued maximum of Microspora from 

 January to May of 1908 folio ws on an exceptionally cold January 

 (Mardi and Aprii also colder than the rule) (p. 67). 



II. — The steady persistence of Conferva from Mardi to June 

 of 1908 corresponds to exceptionally favourable sunshine-condi- 

 tions in the fîrst four months (p. 69). 



III. — The long persistence of Ineffigiata in some quantity 

 in the autumn of 1907seems tocorrespond to particularly favour- 

 able température-conditions in the summer months (p. 80). 



IV. — The prolonged maximum of Eunotia (Himantidium) 



(1) We can scarcely agrée with the gênerai statement made liy Miss Griffiths 

 (Qriffîths, 1U12) on p. 19 ol'her paper on tbe Algae ol'Stanklin Pool,Worcester- 

 shire. 



7 



