212 ClIAETOPHORACEAE 



fluent forms. These large forms have probably been generally 

 referred to Chaetophora tuberculosa, but extended observations in 

 field and laboratory have convinced us that they are merely 

 growth forms of C. elegans. 



The presence or absence of terminal setae should not be made 

 a character for separation of varieties in this species, for plants 

 which possess them early in their growth, lose them later. 



A suspicion was expressed by Wolle, that C. elegans, C. pisi- 

 formis and C. tuberculosa might be stages in the growth of one 

 plant, because he found it difficult at times to separate them. 

 One is inclined to question whether Wolle understood the true 

 character of the species, particularly C. pisiformis. The separa- 

 tion of the species is not a matter of cell measurements, for these 

 are subject to the greatest variation. Practically the only dis- 

 tinction between C. elegans and C. pisiformis as described by 

 Roth, that holds good generally, is in the much more open and 

 loose branching of the former. The issues of the two species in 

 American exsiccatae are badly confused. 



2. Chaetophora pisiformis (Roth) Agardh, Disp. Alg. Suec. 43. 



1812; Syst. Alg. 27. 1 82 1. Grev. Scot. Crypt. Flor. 6: 



Synop. 40. ibid. 3: pi. 130. 1825 (as C. elegans). Kiitz. Spec. 



Alg. 532. 1849; Tab. Phyc. 3: //. 18. f. 3. 1853. Harvey, 



Ner. Bor. Am. 3 : 70. 1857. Rabenh. Flor. Eur. Alg. 3 : ^8^,. 



1868. (?) Cooke, Brit. F. W. Alg. 193.//. 78. f. 1. 1883. (?) 



Wolle, F. W. Alg. 116. //. ioj.f. 1-3, 12-13. 1887. Kirchn. 



Mik. Pflanz. 11. pi. 2. f. 20. 1891. Saunders, Flora of Neb. 



pi. 13. f. 5. 1894. (?) 



Rivularia pisiformis Roth, Neue Beitr. Bot. 1 : 272. 1802.* 

 (Ann. of Bot. 1: 261. 1805.) 



Colonies globose or tuberculose, 2—5 mm. in diameter, usually 

 dark green, rarely confluent, the gelatinous substance dense and 

 resistant ; filaments densely radiating from the center, strict, di- 

 chotomously or less frequently trichotomously branched, branches 

 erect or appressed throughout ; terminal branchlets slender, acute 

 or sometimes setiferous ; cells of main branches about 6-7 ft 

 (5.5—8//) in diameter, 3-6 times as long; terminal cells 4-6/^ in 

 diameter {pi. 38, f 1). 



* Citation from Cat. Bot. 3 : 338. 1806. 



