MacMillan: OBSERVATIONS ON PTERYGOPHORA. 729 



cidedly flattened, measuring 9 mm. in width by 3 mm. in thick- 

 ness. The pinnae do not stand always directly opposite each 

 other, although this in general is their position. Abortion of 

 one pinna of the pair may be observed in this plant at two points. 

 The base of the pinnae is more attenuate than that of the cen- 

 tral lamina. The holdfast is partly cut away, but is flattened 

 out and compacted much more than in plant B. 



Plant " D." This plant was collected in July, preserved in 

 formalose, and brought to Minneapolis for study. It was found 

 growing with several others about twelve feet below the surface 

 of the water at low tide. The stipe from the holdfast to the 

 lowest pinnae is 2 meters in length. From the lower pinnae to 

 the base of the central lamina is i dm. while the central lamina 

 is 1.5 meters in length. On each side of the stipe, extending 

 along its margin for a little less than a decimeter, are the tufts 

 of lateral pinnae, twenty on each side. The longest pinna with 

 uneroded end measures i meter, but pinnae with eroded ends 

 are present, 1.5 meters in length. The breadth of the central 

 lamina is i dm., the midrib being 4 cm. broad. The broadest 

 pinna measures 7.5 cm. from margin to margin. All margins 

 of full grown pinnae are undulate. This character is especially 

 marked in the central lamina. One difference between a plant 

 of the age of " D" and a younger form such as " C" lies in 

 the distance between the adjacent pairs of pinnae. In plant 

 " C," for example, the upper pinnae are three cm. apart along 

 the stipe and this character is also indicated in Ruprecht's 

 plate. In an older plant, such as "D, "the pinnae are very 

 much crowded together, so much so, indeed, that they crowd 

 each other out of a strictly marginal position. The fully de- 

 veloped pinnae, in " D " are all massed within a linear distance 

 of 5 cm., while in " C " they are distributed over twice as much 

 space. 



The stipe in this specimen is 5 cm. in diameter, 2 dm. above 

 the holdfast. Near the holdfast it is i dm. in diameter. Nearer 

 the pinnae it becomes flattened in cross section, first appearing 

 as elliptical, then as lenticular, the edges becoming sharp 2 dm. 

 below the lowest pinnae. Along the sharp edges the scars ol 

 pinnae which have been sloughed off are abundant. The stipe 

 in the region of pinna attachment is 3 cm. broad and 7.5 mm. 

 thick. The stipes of the full-grown pinnae are 4 mm. in diameter 

 and the base of the central lamina is i cm. broad and 3 mm. in 



