MacMillan : Observations ox Nereocystis 



293 



noted that the secretion-cells seem to line all sides of the mucilage 

 duct in young lamina while in young stipe they occur only on the 

 side of the duct which is toward the central cylinder. The occa- 

 sion for this seems to be explained by some of my sections which 

 show the first division-wall of the primitive secretion-cell parallel 

 with the face of the lamina instead of perpendicular to the surface 

 as in the stipe. The cleft then arises between these two small 

 cells, one lying peripherally and one centrally. But in the stipe 

 the first cleft appears in a plane perpendicular to the surface and 

 not between the two primitive secretion-cells, but between the' cells 

 just peripheral to them. I do not like to speak with positiveness 

 upon this point since It Is at variance with the results of previous 

 investigations upon other genera, and but a few of my sections are 



helpful. 



/ 



•As in other 



Lamlnariaceac each lamina of Nereocystis grows by a generally 

 basal area which lengthens in both directions, so that the elonga- 

 tion of the lamina Is neither strictly basipetal or acropctal. The 

 thickening of the lamina, which finally, In old leaves, comes to con- 

 sist of from five to ten cortical layers on each side of the central 

 lamella which is itself made up of a rather compact pith-web tis- 

 sue eight or more layers across, goes on in the general basal area 

 of growth. Old laminae are of a mature type of structure from 

 base to tip since the original thinner primitive tip area has been 

 worn away by the action of the waves and the disappearance of 

 the primitive tip is often to be noted even in veiy young plants 

 less than 12 cm. in length. 



of 



N> 



and origin is altogether typical of the family. The first evidence 

 of the sorus is marked by transverse divisions In the epidermal 

 cells parallel to the surface of the lamina. In this way a double 

 layer of somewhat larger deeper-stained superficial cells and smaller 

 cubical more dimly-stained sub-epidermal cells comes Into exis- 

 tence. The superficial cells elongate Into the club-shaped para- 

 physes which finally come to be- 30-40 mic. in length, about 7 mic. 

 in diameter at the capitate tip and 2 mic. or even less where they 

 join the basal cells. The sporangium originates as an hemispher- 

 ical bud on the basal cell beside the paraphysis. By the attenuation 



