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ment of this form. The scantier représentation of the genus 

 in 1906 as contrastée! with 1907 and 1908 seems again to indicate 

 a dislike for the liigh summer-temperatures that were realised 

 in 1900. It is probable however thai Inefftgiata is adapted to 

 narrower temperature-limits tlian the other four gênera of 

 Protococcaies, since it attains its maximum only on a relatively 

 high température. 



The influence of température does not however altogether 

 explain the periodicity- table of the Protococcaies. It will be 

 évident from subséquent considérations that concentration of 

 the water also plavs a part, some forms {Pandorina, Sphae- 

 rocystis and possibly Ineffigiata) requiring relatively dilute, 

 others {Eudorina, Gloeocystis) relatively concentrated water 

 for satisfactory development. We will take first the forms 

 requiring dilute water and draw attention to the following facts 

 in support of tins conclusion : 



I. — The great scarcity of Pandorina (1) in spring and its 

 absence in the summer of 1906 appearsto be to some extent rela- 

 ted to the low rainfall and exceptional sunshine of the monfh 

 of April (a critical time for the genus) leading to a marked 

 concentration of the water {cf. footnote 3 on p. 01). The saine 

 statement applies to Sphaerocystis. 



II. — In 1907 with uniform rainfall no spécial concentration 

 of the water will hâve taken place, and the conditions were evi- 

 dently more favourable to the two gênera. Thus, in this year 

 Pandorina is more abundant than in 1906 and lasts until Sep- 

 tember with a break in the hottest month (July). 



III. — In 1908 Pandorina shows a similar long persistence, 

 but is rarer than in 1907 ; this may be due to rather higher sum- 

 mer températures and less uniform rainfall. The same remarks 

 apply to 1909. 



IV. — In the case of Sphaerocystis it may be noticed that 

 in 1907 with little rainfall in the first three months it did not 

 reach its maximum till May (?'. c. till after the heavy rainfall 

 of April and May) ; in 1908 with heavy rain already in Mardi 

 it attained to its maximum in April, and the saine applies to 



(1) There is a considérable amount ol'parallel hetween the frequency-table 

 ni Pandorina Auà Chaetophora, although the latter isevidently a more decidèd 

 spring-form. 



