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 tlie 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 b^' de Bary serve to indicate their wide range in size : 



Length, mm. 



Cucuvliita Pepo 370 -.450 



Calarau3 Rotang .... 2.000 

 Potaniogeton natans . . .275 

 Vitis vinifera 6 



Transverse diameter, mm. 



. .045 

 . . .030 -.050 

 . . .025 



281 

 cells. 



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

 They arc always found at tlie ends of the cells, and may 



cells isolateil by maceration ; the septa are in tlieir winter state, i?, Urancliing of 

 cribrose-cell isolated by maceration. r,tangcntial section across a medullary ray, show- 

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

 state. (Wilhelrn.) 



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

 of July) through the bast of a stem 1 cm. thick ; vq, cribrose-cells, the oblique as well aa 

 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.1 



Fig. 73. Cucurbita Pepo Longitudinal section showing terminal sieve-plates at 

 q, q, ami a lateral one at st ; ps^ contracted protoplasm. (Saclis. ) 



