MacMillan: OBSERVATIONS ON PTEKYGOPHORA. 727 



long leaves, often as many as forty in the tuft, hang down 

 beside the stem and as the plant bends from side to side they 

 are swept along the bottom, thus accounting for the erosion 

 of their ends so characteristic of this species. The central 

 lamina is invariably eroded, and only the younger and shorter 

 pinnae are perfect, all the older ones having lost their tips 

 through the constant brushing back and forth on the rocky 

 bottom. The relative lengths of the leaves and of the stem are 

 regulated by this habit of the growing plant and where the 

 surge was most violent plants were to be found with compara- 

 tively long stems and short leaves, but where the surge was 

 less violent the leaves and stem were more nearly the same 

 length, or the leaves might some of them even exceed the 

 stem. 



The general appearance of young Pterygophora plants as 

 seen upon the bottom is not unlike that of Nereocystis. Their 

 attitudes with the erect stem and the dependent leaves are very 

 similar. The older Pttrygopkora plants, from their much 

 more massive stem and shorter leaves, can be distinguished at 

 a glance. 



In order to collect an abundant series of Pterygophora calif or- 

 nica use was made of a tool which may be described as a combi- 

 nation of chisel and hook on the end of a long slender pole, by 

 which the holdfasts were cut and the plant dragged to the sur- 

 face. In this way a sufficient quantity of material was ob- 

 tained from which four plants of different ages are selected for 

 description. 



Plant " A." This is the youngest specimen seen. It meas- 

 ures 12 mm. in length, of which the stipe and primitive disk 

 constitute but 2 mm., the rest being lamina. In this plant the 

 lamina is already eroded distally. It measures 5 mm. across at 

 its broadest part and narrows down abruptly to the stipe, which 

 is 5 mm. in diameter. The primitive disk, almost exactly cir- 

 cular in shape, measures 2 mm. in diameter. At first the growth 

 of the stipe in length is decidedly slow, but when the lamina 

 has become about 20 mm. in breadth the stipe begins to elon- 

 gate. In plants under 30 mm. in length the poorly defined 

 midrib of Pterygophora has not begun to develop and the lam- 

 ina seems perfectly homogeneous throughout. In this respect 

 the plant is in marked contrast with Alaria sporelings, for in 

 them the midrib will have already strongly developed in plants 



