WISCONSIN PHYTOPLANKTON 51 



to considerable variation in the size and delicacy of the apical and 

 lateral lobes, the short stocky form shown in Figure 2 being much 

 more common than the delicate one of Figure 1. 



The incision of the lateral lobes is also subject to variation and all 

 transition stages may be found from those in which only one lateral 

 lobe is entire to those in which there is no incision of the lateral lobes 

 of either semicell. W. & G. S. West follow Johnson in considering 

 this the normal range for the type and think that no varietal distinc- 

 tion can be made on this reduction of the incision in the lateral lobes. 

 The point at which varietal distinctions shall be drawn is a perennial 

 question for the taxonomist and the treatment of the range of varia- 

 tion rests in a large degree upon the personal view-point. My ob- 

 servation of the alga in Canadian lakes, where in certain stations cells 

 with reduced lobes are found to the exclusion of those with incised 

 lobes, leads me to the conclusion that Wolle was justified in consid- 

 ering the forms with reduced lobes a distinct variety. This view is 

 strengthened by the statement of W. & G. S. West that: "this 

 variation is of far commoner occurrence in the United States than in 

 the British Islands ... in Britain we have only met this notable 

 variation of the lateral lobes in the Scottish plankton." 



A most unusual variation from the normal is shown in Figure 3 

 where there are three simple processes on the polar lobe of one of the 

 semicells as well as a lack of bifurcation of the lateral lobules on one 

 haK of the semicell. 



var. SIMPLEX (Wolle) G. M. Smith. PI. 63, Fig. 4. 



Trans. Wis. Acad. Sci., Arts & Lett. 20: 344, pi. 9, figs. 1-5. 1922. 



Micrasterias furcata var. simplex Wolle, Bull. Torr. Bot. CI. 12: 128, pi. 51, 

 figs. 6-7. 1885. 



Micrasterias radiata Hassall. W. &. G. S. West, Monogr. Brit. Desm. 2: 113, 

 pi. 52, fig. 5. 1905. 



Micrasterias furcata Ealfs non Agardh. Johnson, Bot. Gaz. 19: 58, pi. 6, figs. 

 9-14. 1894. 



Lateral lobes of processes of one or both semicells simple and ter- 

 minating in a deeply f ureal e-emarginate apex. (Tychoplanktont.) 



Cells 135 /A long ; greatest breadth 130 /x, breadth at apex of polar 

 lobe 65 ju ; breadth at isthmus 17.5 /a. 



Hill (rrr). 



In the majority of eases all of the lobes are not reduced and one 

 or more has the deep incision of the type. When this is the case the 

 incision occurs in the lateral lobes adjacent to the polar lobe rather 

 than in the lobes adjacent to the sinus. 



