PSALLIOTA CAMPESTRIS 



407 



becomes a light area, and every light area, owing to the develop- 

 ment upon it of spores which have become pigmented, becomes a 

 dark area. A single area becomes alternately dark and light a 



FIG. 142. Psalliota campestris (cultivated ^form). Surface view of 'a piece of 

 hymenium 0-15 mm. long and 0-1 mm. wide, semi-diagrammatically showing 

 a white area surrounded by a dark area. The spores alone have been fully 

 sketched, but the positions of the spore-bearing basidia are indicated by dotted 

 circles. The white area is enlarging at the expense of the dark area : the 

 dotted line indicates the limits of the white area and the arrows the directions 

 of its extension. The basidia at a, b, and c, just outside the dotted ring, have 

 each discharged one of their two spores ; and at a and c water-drops are being 

 excreted at the bases of the remaining spores in preparation for spore-discharge. 

 The basidia at d, e, /, and g in the white area are developing spores which as 

 yet are only from 3 to 15 minutes old but which are rapidly attaining full size. 

 At h the spores are older and of full size but colourless. At i and j the spores 

 are still older and are becoming pigmented. At k, I, and m in the dark area 

 the basidia have developed only one spore each, but the spore has twice the 

 normal volume. At n and o two adjacent basidia have developed spores 

 simultaneously and the four spores in each group have arranged themselves 

 so that they occupy the corners of a square. At p, also, the spores are so 

 arranged that those of adjacent basidia can not come into contact during 

 development or discharge. Magnification, 706. 



number of times in succession during the several days of the spore- 

 discharge period. The actual passage of slow waves of develop- 

 ment over the hymenium of a Cultivated Mushroom was witnessed 

 for a gill kept under continuous observation for eight hours in a 

 compressor cell in the manner described in Chapter II. 



