MacMillan: OBSERVATIONS ON PTERYGOPHORA. 737 



with smaller. Outside of the rings will be found the cambial 

 zone in which regular divisions take place in all three planes of 

 space. Exterior to the cambial zone lies a thin outer cortex 

 composed of cells very much smaller than those of the inner 

 area, provided with thick walls and constituting a kind of bark 

 for the trunk. In some material the general cambial zone can 

 be very distinctly seen, ten or twelve cells in thickness and 

 separated from the epidermis by twenty or more layers. Not 

 infrequently the cells at the periphery of a ring of growth have 

 more densely granular contents than those of the general sec- 

 ondary cortex tissue. Thus, occasionally in the stipe there may 

 arise the anatomical conditions which seem to be more normally 

 characteristic of the holdfast. The photographs of different 

 cross and longitudinal sections which are presented will serve 

 to make these points clear where the description is necessarily 

 difficult to follow. 



The lamina. As before stated only the central lamina is pro- 

 vided with a midrib, the pinnae being quite devoid of such a 

 structure. The midrib of the central lamina arises through an 

 hypertrophy of the cortical tissue, in which th , pith-plate does 

 not seem to partake. The general structure of the lamina as 

 seen in cross section does not present many peculiar features, 

 but is much like that already described for other genera. There 

 is on each surface an isomorphic epidermis composed of small 

 quadrate chlorophyll-containing cells, and these merge insensi- 

 bly into the subepidermal tissue, which in some instances is 

 two or more layers in depth. The cells then become much 

 larger in diameter and the contents less dense. Among these 

 cortical cells occasional very large polysaccharid idioblasts are 

 found, and in the chocolate-colored pinnae of plant " C," these 

 cells are very numerous and densely packed with spherical 

 bodies, doubtless belonging to the category of reserve carbohy- 

 drates. Owing to the nutritious character of such pinnae, they 

 are very commonly perforated by animals, sometimes giving a 

 colander appearance like that of Agarum, and covered with 

 epiphytic and endophytic vegetation, a further study of which 

 should be made. These reservoir cells may perhaps be packed 

 with food materials previous to the production of sori and the 

 polysaccharids utilized in the elaboration of the sporangia and 

 paraphyses. In any event they seem to be emptied of their 

 contents underneath most of the soral areas that I have exam- 



