PSALLIOTA CAMPESTRIS 427 



varies from about five minutes in no. 41 to about eight hours in 

 nos. 24 and 32. Spores which are of full size but colourless are from 

 forty minutes to two hours and forty minutes old (nos. 53 and 57). 

 Spores which are undergoing pigmentation are from two hours 

 forty minutes to four hours and forty minutes old (nos. 61, 3, and 

 5). Spores which are fully pigmented are from four hours and forty 

 minutes to eight hours old (nos. 11, 16, 24, 32). These ages are 

 approximations based on studies already recorded. The contents 

 of the basidia are not shown but, if they were, we should see that 

 the bodies of nos. 41, 44, and 48 were practically full of protoplasm 

 and that the bodies of nos. 24 and 32 were empty. We should 

 observe stages in the progressive emptying of the basidium-contents 

 into the spores in nos. 53, 57, 61, 3, 5, 11, 16, and 24 : we should 

 note the origin and increase in size of a basal vacuole in the 

 basidium-body, and its extension upwards until it filled not only 

 the whole basidium-body but also the sterigmata except perhaps 

 their tips. Most of the basidia are bisporous, but two of them, 

 nos. 48 and 57, are monosporous. The solitary sterigma of each 

 of these is situated in line with the axis of the basidium-body. 

 The spores of the monosporous basidia develop unilaterally on the 

 ends of their sterigmata, and each possesses the usual hilum ; but 

 they differ from the spores of the bisporous basidia in size. If 

 one compares the spore on no. 57 with the spores on nos. 11, 53, or 

 61, one perceives that the former is distinctly longer, somewhat 

 broader, and of about twice the volume of the latter. 



Nos. 3 and 5 show the typical arrangement of the spores on 

 any two very closely adjacent basidia which develop their spores 

 simultaneously : the four spores are situated at the corners of a 

 square or rectangle (cf. Fig. 146, lower right-hand corner at b, 

 p. 416). This prevents any jostling of the spores during their 

 development and discharge. The positions of the spores are de- 

 cided by the positions of the sterigmata at their first origin ; and, 

 as we have seen, the positions of the sterigmata appear to be 

 decided by the positions which the centrosomes of the daughter 

 nuclei in the basidium-body take up after their formation. 1 It 

 seems probable, therefore, that the position of the spores in such 

 1 Cf. p. 420. 



