Holtz : OBSERVATIONS ON PELVETIA. 41 



Methods: fixing and mounting fluids. Material fixed and 

 preserved in formalin was employed. This was washed in 30 

 per cent, alcohol, as fresh water alone caused injurious swelling 

 of the laminag. The material was then passed into higher per 

 cents of alcohol to harden and dehydrate. The complete de- 

 hydrating seems to cause tensions in the body of the plant result- 

 ing in tearing apart of pith cells, the intercellular jelly giving 

 way. But occasional very perfect pith sections may be thus 

 obtained nevertheless, and by comparing with sections cut from 

 70 per cent, or 80 per cent, alcoholic material and mounted in 

 water or glycerine the nearly natural appearance of these cells 

 can be observed. 



Most of the drawings were made from dehydrated material, 

 and must therefore be somewhat unnaturally contracted. Where 

 water or glycerine mounts were made and drawings from them, 

 it is so indicated in the notes explanatory of the plates. The 

 gelatinous walls swell greatly in glycerine (as compared with 

 alcohol) but as the cross-sections of the lamina and stipe, for 

 instance, have practically the same dimensions as the formalin 

 material it may be assumed that the glycerine mounts give a 

 truer picture of the tissues than do the balsam mounts. 



Sectioning. Most of the sections, especially the serial 

 sections illustrating conceptacle development and the growing 

 point, were made with a microtome from material imbedded in 

 paraffine. After the work of hardening is once started this 

 method is probably as rapid as any where imbedding is neces- 

 sary. Some sectioning was done with a hand microtome, the 

 75 per cent, or 85 per cent, material being held in a pith clamp. 

 Such sections were mounted generally in glycerine. These 

 sections however showed a tendency to curl more than paraffine 

 sections. 



Staining, A variety of stains were tried. Many of the 

 ordinary wall stains proved entirely ineffectual. At length the 

 following stains were selected as the best. 



Fuchsine and methyl violet is perhaps the most generally 

 useful. This mixture stains quickly and deeply. Washing 

 cautiously in acid alcohol brings out different effects. Only 

 a little washing leaves the gelatinous matrix slightly stained, the 

 inner walls stain deeply, while the cell contents again take a 

 slight coloring. Differentiation is brought out nicely, generally 

 by more washing, in the conceptacular parts. The granular 



