242 



METHODS IN PLANT HISTOLOGY 



Stypocaulon affords an excellent study of the structure of cytoplasm. 

 The Chicago formula, on page 28, is good for fixing this or any of the 

 small members of the brown algae. The centrosomes and radiations 

 stain particularly well with Haidenhain's haematoxyUn or with the 

 safranin, gentian violet, orange combination. For these immense api- 

 cal cells, it is a good plan, when the material gets into xylol, to break 

 off pieces 6-12 mm. long, which will lie flat in the paraffin. If you try to 



cut a whole tuft, most 

 of the cells will be cut 

 so obliquely that they 

 will be worthless. 



Ectocarpus. — Dur- 

 ing most of the year, 

 Ectocarpus will have 

 only gametangia: the 

 sporangia are at their 

 best in December and 

 January. For a short 

 time, during the cold 

 season, the plant bears 

 both sporangia and 

 gametangia. A 10 per 

 cent solution of forma- 

 lin in sea water is a 

 good fixing agent for 

 all stages, if material is 

 to be mounted whole 

 (Fig. 59). Stain some 

 in iron-alum haematoxylin, and some in phloxine and anihn blue; then 

 mount from both lots under each cover. 



The Chicago formula is better for paraffin sections. 

 Desmotrichum. — Forms as large as Desmotrichum- can be handled 

 like Ectocarpus, but care must be taken not to overstain. 



Laminaria. — In such large forms, small portions showing the struc- 

 ture and development of the thaUus and also the reproduction should 

 be cut out with a razor and then placed in the fixing agent. The spo- 

 rangia of Laminaria stain very deeply and quickly. Iron-haematoxylin 

 is good, but be careful not to overstain. After this stain is just right, 

 about 3-5 minutes in alcohohc safranin will stain the mucilaginous 

 structures and add to the value of the preparation. 



Fig. 59. — Ectocarpus: A, sporangia of various ages; B, 

 gametangia, three of them nearly mature. Fixed in 10 per cent 

 formalin and stained in iron-alum haematoxylin. X280. 



