92 



MORPHOLOGY OF THE CELL. 



very soft and colorless. Owing to their yielding character, it is 

 not easy to make satisfactory sections for their demonstration, 



from fresh material ; it is better 

 to keep the material in alcohol 

 for a while, or to dry it care- 

 fully, as Russow advises. All 

 sections, to show the sieve-cells, 



79. 



73 



must be veiy thin. The following measurements of single large 

 cells given by de Bary serve to indicate their wide range in size : 



Length, mm. 



Cucurbita Pepo 370 -.450 



Calamus Rotang .... 2.000 



Potamoseton natans 



.275 



Transverse diameter, mm. 

 . .045 

 . .030 -.050 

 .025 



A r itis vinifera . .6 



281. The sieve-plates occur at the points of contact of sieve- 

 cells. The}' are always found at the ends of the cells, and may 



cells isolated by maceration ; the septa are in their winter state. 7>, branching of 

 cribrose-cell isolated by maceration. C, tangential section across a medullary ray, show- 

 ing the transverse anastomosis of cribrose-cells ; the callus at the septa is in its winter 

 state. (Will) elm.) 



FIG. 72. Cribrose-cells in Vitis vinifera. Longitudinal tangential section (beginning 

 of July) through the bast of a stem 1 cm. thick , i:q, cribrose-cells, the oblique as well as 

 one horizontal perforated septum cut longitudinally. The face of one septum, however, 

 is shown at the upper part of the figure; rm, medullary rays. (De Bary.) 



FIG. 73. Cucurbita Pepo Longitudinal section showing terminal sieve-plate? at 

 Q, q, and a lateral one at si ; ps, contracted protoplasm. (Sachs.) 



