502 



BOTANICAL GAZETTE 



[DECEMBER 



(13), in his study of aerenchyma, came to the conclusion that the 

 cells adhere by the thickenings of the walls, while the pits remain 

 free. Mangin (19) believes the split to be due to a gelatinization 

 of pectates in the wall, which substances, in consequence, line 

 the intercellular space thus formed. 



A study of the stellate parenchyma of Juncus effusus leads me 

 to the conclusion that Schwendener has given the correct explana- 

 tion of the origin of this type of cells. All cells pass through a curve 

 of growth. The center is the oldest part of the pith and reaches the 

 mode of the curve first. As the growth in this region becomes 

 slower, the outer parts are approaching the mode of the curve. 



F 



Fig. 5. — Scirpus validus: longitudinal section of young stem: diaphragm with 

 cross-section of cross-bundle; nuclei as in fig. 2; s, cells of space; p, partition cells; 

 b, cross-bundle; d, ordinary diaphragm cells; /, food storage cells; Xi75- 



Thus the growth of the central cells cannot keep pace with the 



and thev are. in 



arms 



The slower the growth the greater the proportion of 



arms 



diameters 



many pith cells at the same stage of development, and 



similar 



from 



stem, to 21 . 5 11 a little farther back, and to 17 . 1 



In any one section the cells at the center are at a much la 



development than those toward the outside of the stem 



ix still farther back 



