248 METHODS IN PLANT HISTOLOGY 



sistency, the time must be measured in seconds, rather than in minutes 

 or hours. 



For many others, the times are longer. For Plocamium, 6-8 hours; 

 Nitophyllum and Rhodymenia, 8-10 hours; Gelidium, overnight; Ban- 

 gia and Porphyra, 24 hours; Nemalion, 24 hours or longer. 



After washing 24 hours in sea water, an hour in equal parts sea water 

 and fresh water, and an hour in fresh water, follow the close series of 

 alcohols described in the chapter on the paraffin method. For fila- 

 mentous forms, use Petri dishes for the alcohol and xylol series and 

 keep the forms as straight as possible. After 24 hours in 85 per cent 

 alcohol, test the material to determine whether it is sufficiently hard- 

 ened. With forceps, take the base of a plant like Polysiphonia and 

 move it gently back and forth in the direction of the long axis. If it 

 keeps its shape, it is ready to go on: if the branches bend back toward 

 the forceps, keep it in the 85 per cent alcohol until there is no bending. 

 This is also a test for any other filamentous algae or fungi. 



Thirty minutes in the bath should be long enough for any of the 

 brown or red algae, whether coarse or filamentous. It takes about 30 

 minutes to make 4 changes of paraffin, and so the time cannot be 

 shortened much for delicate forms, and it is sufficient for coarse forms 

 like Gigartina. 



Batrachospermum. — This is a green, fresh-water member of the red 

 algae. It is not very uncommon in small streams. Fix in the formalin 

 solution or in the chromic solution recommended above. It can be left 

 indefinitely in the formalin solution. In the chromic solution, it should 

 fix overnight, or 24 hours. Iron-alum haematoxylin seems to be the 

 best stain, both for material mounted whole and for sections. In 

 mounting whole, tease out small portions and still further dissociate 

 the filaments by tapping smartly on the cover. 



Nemalion. — Fix in the formalin solution recommended above. In a 

 10 per cent formalin solution, Nemalion has kept its color for 15 years. 

 In the chromic solutions, fix for 24 hours. Nemalion does not break up 

 like so many delicate red algae. For studying fertilization, Wolfe used 

 the following method : 



Young tips were crushed in water under a cover glass and on a slide that 

 had previously been treated with fixative; the cover was then removed, and 

 the water on the slide allowed to evaporate. The gelatinous nature of the 

 wall prevents the contents of the cell from being affected by this treatment, 

 even when the albumen has hardened sufficiently to hold the filaments 

 firmly in place. 



