25 



towards the end of November, but principally from May through 

 October. There are but slight indications of a vernal pulse, which 

 on May 25, 1897, culminates at 3,600,000. The major pulse cul- 

 minates at 10,800,000 on August 9, 1898. In the low water and 

 prolonged high temperatures of 1897 the major pulse continues 

 through September, culminating on the 21st at 32,000,000. The 

 average number in this year was about four times as great as in 

 1898. The temperature limit is 43, though occurrences are few 

 and numbers small below 65. The maximum development appears 

 within the period of maximum heat, and towards its close. It is 

 characteristic of the plankton of late summer and early autumn. 



Crucigenia rectangularis Nag.* Average number of colonies, 

 7,153,846. Recorded in all months but March and April, but spar- 

 ingly from November till May. In 1897 pulses appeared in August, 

 September, and October, attaining 32,400,000, 57,600,000, and 

 118,800,000, respectively. In 1898 there was but a single pulse 

 in August, of 158,400,000. It was more abundant in the former 

 year. It is present continuously in large numbers from July to 

 October, though in 1897 the impetus of the unusual development 

 was manifested by the continuance of the species even into Janu- 

 ary. The optimum temperatures lie above 70, in the latter part 

 of the period of maximum heat, though the species has been found 

 in the plankton throughout the whole range of temperatures. The 

 abrupt decline in numbers occurs between 65 and 40. It is char- 

 acteristic of the plankton of late summer and early autumn. 



Golenkinia radiata Chodat. Average number of colonies, 

 519,231. It appears most abundantly during the April-May plank- 

 ton pulse (7,200,000) and again, in increased numbers, at the end of 

 August, thus suggesting a vernal and a late summer maximum. It 

 seems to be most abundant at about 60, a temperature somewhat 

 below the optimum for the two preceding species. Two occur- 

 rences in December, 1896, and large numbers in August indicate its 

 adaptability to the full range of temperatures. 



Oocystis naegelii A. Br.* Average number, 207,692. In 1897, 

 much more abundant (average, 4,243,235). Present in numbers 

 (over 5,000,000) from the end of May till the end of September. 

 In 1897, pulses of 10,800,000, 46,800,000, and 24,750,000 appear in 

 May, July, and September respectively. Both numbers and oc- 

 currences are much less in 1898. The optimum conditions thus lie 



