32 MINNESOTA BOTANICAL STUDIES. 



similar that no change is noticeable in passing from one to the 

 other. In the lamina proper, however, the pith cells branch 

 more and the rows of cells have a more meandering course, 

 and there is more anastomosing. The intercellular jelly is de- 

 veloped here more than elsewhere in the plant. Due to this 

 and some to the branching of the cell rows the blade is much 

 thicker than the stipe. 



The cortex and epidermis are similar to those of the stipe. 

 The crowding growth of the conceptacles disarranges the order- 

 liness of the cell arrangement in the cortex and epidermis. 

 Cross and longitudinal sections of the lamina resemble those of 

 the stalk closely, except for the differences just mentioned, and 

 for the conceptacles {-Fig- J shows a partial cross-section of a 

 lamina). 



The grozuing point. — In the tip of the maturer laminae no 

 definite growing point can be found. There still is some growth 

 and cell division going on here in the outer cortical cells, and 

 in a mature lamina this is probably the youngest and tenderest 

 portion. It is here that the lamina begins to burst when placed 

 in fresh water. Even at the sinus between the lobes of the 

 lamina no growing point can be found in older laminae. This 

 is the place where the growing point once was. But the growth 

 seems to have stopped here first and continues for a time longer 

 toward the ends of the lobes. 



If a young frond is examined, one in which there is as yet 

 no difference between stem and blade, a slight notch or dimple 

 is visible at the top. This notch deepens in older fronds, and 

 if a section is made through the somewhat flattened stipe, par- 

 allel with the flat surface and through the axis of the frond, a 

 large apical cell is seen at the base of the sinus {PL ^Y., Figs. 

 75, 16). This apical cell is an epidermal cell. It is in the 

 shape of a truncated pyramid, with the truncated end to the top 

 or pointing outward. The apical cell is two or three times as 

 large as the other epidermal cells, and is otherwise markedly 

 distinguished by great richness and granularity of contents, and 

 by the absence of chromatophores. The adjacent cells share 

 these characteristics to a less degree. They show a diminution 

 in the granularity of the protoplasm, and color grains begin to 

 appear in all but the latest cutoff. 



The apical cell, as seen in vertical section, cuts off daughter 

 cells in succession, a lateral, then a basal, and then a lateral 



