164 MINNESOTA BOTANICAL STUDIES. 



In many places where there is almost no elevation of the sur- 

 face a small group of tetraspores is distinctly seen in section. 

 Staining with iodine brings out the distinction between tetras- 

 pores and the surrounding cells very clearly. 



A peculiar feature of the nemathecia is the pore-like break in 

 the cuticle just above the group of spores. This W'as seen in 

 even the smallest nemathecia, and in the larger ones several 

 were often present. A full-grown nemathecium rises from 25-37 

 mic. above the level of the thallus, and an irregularity in the ar- 

 rangement of the cortex cells is noticeable at the apex, suggest- 

 ing a rupture as a result of the crowding upward of the spores. 

 The spores measure 12-20 mic. by 10-15 rnic 



Wille* makes a physiological distinction between the pith and 

 cortex regions, considering the former as conducting tissue and 

 the latter as assimilative. Some interesting results were brought 

 out by iodine staining in connection with this view. 



Sections of the holdfast, stipe, lamina, cystocarp region and 

 nemathecia were placed in an iodine solution for half an hour, 

 then w^ashed with water, with the following results : The hold- 

 fast simply shows a general yellowish staining of the cell walls, 

 showing there is no starch present in that region, as would be 

 expected from its evident mechanical function. The stipe like- 

 wise showed a slight yellowish staining of the walls, but no cell 

 contents in accordance wath its function as a supporting and 

 conducting area. 



In the lamina the sections used were longitudinal ones. The 

 central elongated cells remained colorless ; in the inner cortex 

 cells marking the transition in shape from the central to the 

 small peripheral cells the contents stained a deep purple, in- 

 dicating the presence of starch. The four or five outer rows 

 showed the cell contents stained yellowish brown. These are 

 the cells containing chromatophores. These results suggest a 

 confirmation of Miiller's interpretai.sn of the physiological sig- 

 nificance of this area, inasmuch as they are evidently concerned 

 with the food supply. 



In the cystocarp region the outer layers of cells containing 

 rhodoplasts stain yellowish brown as in the lamina ; the rest of 

 the pericarp and the spores stain a deep violet, but the thin- 

 walled cells separating the groups of spores stain yellow. This 

 brings out the structure of the central spore region better than 

 any of the other stains used. 



* Wille, N. Nova Acta Acad. Leop. -Carol. Nat. Cur. 52 : 49-100. _^/. 3-^- ^^91- 



