Holtz: OBSERVATIONS ON PELVETIA. 33 



on the other side (see diagram, Fig. 16). The daughter cells 

 quickly divide again and again, but more frequently in a lateral 

 direction from the apical cell than downward. The cells in 

 these lateral zones divide more rapidly in planes transverse to 

 the axis of the lamina. In this way the zone of most rapid 

 growth extends out laterally and upward from the apical cell 

 and soon grows up ahead of the growing point. As a result 

 there is the bifurcated lobe. 



Differentiation into the long pith cells begins only three cut- 

 offs below the apical cell. In the wings it does not begin so 

 soon. The zone of cells in the wings retains its power of fis- 

 sion longer than the cells below the apical cell. 



The cells of the epidermis and the cortical zone attain the 

 characteristics of these tissues but a short distance from the 

 apical cell. 



The outer cortical cells throughout the plant are capable of 

 dividing and seem to constitute a kind of cambium around the 

 plant. This meristematic nature of the cortex is most highly 

 developed in the lobes of the young lamina near the growing 

 point. It is also well developed where conceptacles form and 

 in the marginal parts of the holdfast. 



The cuticular sheath that covers the whole plant is very thick 

 over the delicate growing point, being about as thick as the 

 length of the epidermal cells beneath it, no doubt serving as a 

 protection. 



It is customary to speak of the rows of cells in the plant as 

 hyphae. But when the origin of these cells is considered, that 

 they are derived directly or indirectly from a single apical cell, 

 the idea of their hyphal character seems a little incongruous. 



On the development of the conceptacle. As before noted 

 the conceptacles show an intimate connection with the cortex. 

 Sectional views prove the cortical origin and nature of these 

 structures. 



The first indication of the beginning of a conceptacle is seen 

 to be the cutting off of a basal layer of cells from the lower end 

 of a few adjacent epidermal cells (PL F., Fig. //). These 

 basal cells in turn divide periclinally and radially to form a 

 little pad of meristematic cells beneath the epidermis, around 

 which the cortical cell-rows are deflected. Directly over this 

 mass of basal cutoffs, usually in the center, one or more epi- 

 dermal cells begin to show signs of disintegration and collapse. 



