170 INTRODUCTION TO THE STUDY OF FUNGI 



an entirely exposed surface without great risk of destruction ; 

 but by means of this arrangement they thrust themselves up- 

 wards through protecting channels, lined everywhere with a 

 lubricative fluid, so that their movements are facilitated as well 

 as protected. It is an undoubted fact that all the asci of an 

 hymenium are not developed at once, but proceed for some 

 time in a regular succession from the subhymenial tissue. At 

 first the asci are slender, gradually ' increasing in volume as 

 they rise, but until they have attained their full height their 

 contents are plastic and granular. Having approached their 

 adult stature, the differentiation of the protoplasm takes place ; 

 gradually the outline of the sporidia is indicated, commencing 

 at the summit of the ascus and progressing downwards ; and 

 finally the sporidia are formed. It is well to bear in mind 

 that the terminal sporidia are the first to be matured, and this 

 is conspicuously evident when the sporidia are ultimately 

 coloured; under favourable circumstances a delicate gradation 

 of colour will be observable downwards through the whole 

 series. It has already been remarked that it is of rare 

 occurrence that the asci should reach by their apices the sur- 

 face of the disc. As a rule the paraphyses, being the longest, 

 extend above, and still protect the asci. The swollen or 

 clavate tips compensate to some extent for the space occupied 

 below by the asci, and the surface is still maintained imper- 

 vious. In cases where the tips of the paraphyses are not 

 clavate but filiform, they are not unusually branched in 

 their upper portion, which only adds to their volume ; and in 

 some cases the extremities are bent, curved, circinate, or inter- 

 woven, so that still the whole disc is covered, and no openings 

 left above the apices of the rising asci. Undoubtedly the 

 apices of the asci are always most free from pressure or 

 restraint, which is essential to the free discharge of the mature 

 sporidia. It may sometimes be seen on the field of the micro- 

 scope that, as a mature sporidium is expelled from the apex of 

 its ascus, the clavate paraphyses which surround it are parted 

 by the force of the eviction, but immediately resume their 

 old position again with a jerk, as if impelled by their own 

 elasticity. These observations have been made, of course, on 

 such Ascomyceteae as have the disc exposed, but by analogy we 



