698 GENERAL TECHNIQUES FOR CLASSES OF PLANTS 



strates the form of diatom markings by impregnating the frustules 

 with gelatin, staining with iron ha^matoxyhn and mounting in 

 70 per cent, glycerin, which has the same refractive index as the 

 diatom silica. 



1385. Rhodophyceae are difficult technically. The use of 

 formalin (unless neutral and stored in the dark) should be avoided, 

 especially with segmented forms, as it leads to disintegration. It 

 is best to use chrom-acetic or formalin-acetic-alcohol for general 

 fixation and preserve in 70 per cent, alcohol. Westbrook {Ann. 

 Bot., xlii, 1928, p. 149) also uses picro-uranium nitrate. Use the 

 weaker Flemming solutions for filamentous forms and fix for short 

 periods (a few minutes to one hour). Wash while dehydrating 

 through the alcohols by close stages and keep in the dark. The 

 large coenocytes of some (Griffithsia) need special care. 



Safranin and anilin blue give a good contrast ; nuclei purple, 

 chromatophores light blue and cell walls pink. 



Section fleshy forms by freezing or imbedding in soap ; paraffin 

 often badly distorts them. Sturch {Ann. Bot., xl, 1926, p. 585) 

 cuts Choreocolax in frozen mucilage. 



Calcareous species are especially troublesome. For general 

 morphology and histology fix and decalcify in a large volume of 

 chromo-acetic. Fix in a rather large volume of Flemming's for 

 cytology and rapidly remove the COo with a vacuum pump, 

 adding additional chromo-acetic as the original becomes exhausted. 

 Massive sorts, e.g. Lithothamnion, seem impossible. 



1386. Philip's Method for Developing Procarps and Cystocarps 

 {Ann. Bot., ix, 1895, p. 303). Fix living material with chromo- 

 acetic or aqueous iodine and place in 10 per cent, glycerin after 

 staining, preferably with Hofmann's blue. A little eosin added to 

 the glycerin will also stain the specimen. No stain is required in 

 many cases. The walls of the procarps are gelatinised and swell 

 greatly, so that the intercellular connections are readily visible. 



Cryptonemiales. Split tips lengthwise exactly through the 

 apex with a sharp razor. Lay both halves split side downwards 

 on a coverslip, invert upon a slide and add water, tinted with 

 eosin, from the side. 



1387. Sporelings and Epiphytes. Culture on slides, fix and stain 

 and mount in position. Use perfectly clean slides. If the organisms 

 do not easily make a firm attachment, grind the slide slightly on 

 one side with a sand blast or emery or etch with hydrofluoric acid. 



Butcher {Ami. Bot., xlvi, 1932, p. 813 ; New Phijt., xxxi, 

 p. 289) uses five glass slides 3x1 in. in a metal photographic frame 

 secured to the river bed for the collection of algae and the detection 

 of sewage fungus {Sphcerotilus natans). The slides are examined 

 after four weeks. 



For positively phototropic organisms (zoospores from Chceto- 

 phora, (Edogonium, Stigeoclonium, Viva, Ulothrix) place the 



