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THE AMEBIC AN X. ! TURA LIST [Vol. XLVIII 



tion to their depth. If the seventh leaf has one sinus 

 in each margin, the eighth and ninth usually have two, 

 the tenth and eleventh, three, and so on, until the mean 

 of six is reached. As the lobes increase in number, they 



not only become narrower but the sinuses do likewise. 

 This is the result of a gradual increase in the angle 

 between the lower margin of the sinus and the midrib. 

 In the eighth leaf the lower margin forms an angle of 

 about 90 degrees with the midrib, causing the formation 

 of a primary lobe, triangular in shape and with an upper 

 angle of about 45 degrees, instead of the 90-degree angle 

 found in the first lobe. In older leaves the angle between 

 lower margin of sinus and midrib may increase to 110 or 

 even 120 degrees. The climax leaves therefore get to 

 resemble more and more those of rhomboid ea, especially 

 since the distal margin of the sinus, from the tenth leaf 

 on, exhibits a number of denticulations which, in older 

 leaves, especially of one of the forms (Treleaseana), 

 tend to become incisions, so that secondary lobes are 



