22 HENRIK PRINTZ [1920 



oonleiits of same few cells liave formed ovoid zoosj)ores by isiinul- 

 laneous divisions. 



This alga thus having zoospores, a way of reproducllon thait is 

 not known lo lake plaoe in tlie true genus Protococcus — as I consi- 

 (ler the stialemenls of this as very problematic — and as llie alga in 

 qnesliion fuilher is kcking Ihe divisions so characteristic oif Proto- 

 coccus, it differs so widely and in so essential characters, Ihait il 

 appeans to belong to a totally cMfferent genus. I therelore provi- 

 sionall}' class it as Pleurastrum lobatum, and give the foUowing 

 <liagnosis: 



CelluUs inflatis, rotundatis, viilgo 7 — 12 ^u, raro usque ad 15 jj, 

 diametro, pleriimque colonias 2 — A cellularum, vel majores in uno 

 piano sit(u-um formantilnis. Membrana hijalina, tenerrima et levi, 

 raro tenuiler crenulata. Chromatophoro 1, raro 2, paricfali, lamini- 

 formi, niargine vulgo irregulariter lobnlo, tatere uno partern 

 acbroam vulgo relinquente. Pijrenoidibus nullis. Nucleo pro ratione 

 magno, centraliter silo. Propagatio cellulis in plana duo inter 

 se perpendicularia successive divisis. Zoosporis ovatis divisionibus 

 simultaneis contentus cellularum ortis, membrana materna tenui 

 dirupta liberis. Zoosporis 2 — 5 jn longis. 



It is extraordinary that such an exceedingly frequent sipeoies, 

 apparently occurring nearly all over the world, has not earlier been 

 more oompLetely known. As a rule it will be niet with only as 

 2 — 3- or 4-celled coloniies, in which the morphological conformity to 

 the genus Protococcus is absolute. That the divisions take place in 

 two, direetions only, is, accoiidingly, not possible to obscrve in such 

 cases, as the cells after the divisions disintcgrate to quickl}'. In 

 some samples, however, I have not unfrequently mel with this 

 species as larger colonies, an appearance possibly owing to extemal 

 conditions. At times, also solitary spherical or ovoid cells are to be 

 found. Fig. 164, pi. IV ishows a solitary cell in zoospore-fonnation. 

 Fig. 165 — 168 represent progressiye stages of csll-divisions. 



The membranes in this alga are very thin, hyaline and smooth. 

 Just as in other subaérial algae, I have also in this species at times 

 observed cells with finely crenulate membranes, however. The size 

 of the cells is usually 7 — 12 fi, sometimes up to 15 fi in diameter, 

 and down to 5 — 7 // in diameter. The divisions are rather irregular, 

 and colonies consisting of three cells are not unfrequently lo be 

 seen. The chromatophore is cup-shaped, with partly incised edges. 

 There is no pyrenoid. The zoospoire-formation has not been oommon 

 in any of the sam])les, and is certainly rare in free nature. It is 

 ]Jossible, or even probable, that this only is limited to certain 

 seasons, or is dependant on particular external conditions. It 

 appears from the pictures that the formalions of zoospores may 

 take place in one or sevaral cells of the same oolony at the same 

 time. The regular way of reproduction is, undoubtedly, by cell- 



