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, 



must be very thin. The following measurements of single large 

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



Cucurbita Pepo . . 

 Calamus Rotang . . 

 Potamogeton natans 

 Vitis vinifera . 



Length, mm. 



.370 -.450 . 

 2.000 



.275 



Transverse diameter, 

 . . .045 

 . . .080 -.050 

 .025 



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

 cells. They are always found at the ends of the cells, and may 



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

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

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

 state. (Wilhelm.) 



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

 of July) through the bast of a stem t cm. thick , /, cribrose-cells, the oblique as well as 

 one horizontal perforated septum cut longitudinally. The face of one septum, Imwi-ver, 

 i* slmwn at the upper part of the figure; rm, medullary rays. (De Bary.) 



FIG. 73. Cucurbita Pepo Longitudinal section showing terminal sieve-plates .it 

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



