MONOGRAPH OF THE LABOULIiEXl A( I , I ,. 



231 



the wall-cells, although quite independent of it, and the same is in general true of all 

 the genera. In forms in which, like Ceratomyees, the wall-cells become very numer- 

 ous, a corresponding increase in the number of the canal-cells takes place ; although 

 the number formed may be fewer, as is indicated in Plate XXIV, fig. 8, which repre- 

 sents the growing apex of a perithecium in section, the divisions of the wall-cells (to c) 

 bring evidently more numerous than those of the canal-cells (cc). There seem, also, 

 to be certain variations in the relative position of the canal-cells. In Sphaleromyces, 

 for example (Plate III, fig. 2), the cells [x) are probably the lower canal-cells which 

 have, by pushing between the wall-cells, assumed an apparently external position ; and 

 some similar modification of the more normal course of development may account for 

 the peculiar arrangement of the cells at the tip of the perithecium in this genus, when 

 seen antero-posteriorly as in fig. 1. It is not improbable that there are, in certain 

 east's, variations of the course of development above described : yet in all the instances 

 in which a careful examination has been made, it seems to correspond in all essentials. 



While the wall-cells of the perithecium have a definite protective function, persist- 

 ing and forming an envelope around the ascus and spore masses, and regulating and 

 directing the dispersion of the spores; the inner series, as we have seen, performs an 

 entirely different function which may well be compared, in so far as concerns the cells 

 which I have called the parietal cells, to that of the so-called tapetal cells in the sporangia 

 of the higher cryptogams ; while the cells which I have called the canal-cells bear a 

 similar resemblance in function to the neck-cells, for example, of an archegonium. It 

 is needless to say, however, that there is not the slightest homology between the two 

 structures in either case. The function then of the parietal cells is to make room for 

 the developing ascus masses, and allow them to float free within the cavity of the 

 perithecium ; while that of the canal-cells is to afford a channel of exit by means of 

 which the spores may make their way out through the pore of the perithecium. For, 

 as we have seen in the case of Stigmatomyces, which is typical of the family generally, 

 the growing ascus masses press upon and destroy not only their own connections with 

 other cells above and below, but also the thin-walled parietal cells around them ; while 

 the mass of mature spores, which is constantly being pushed upward, has a similar 

 effect upon the canal-cells, the latter, as a rule, having disappeared entirely when the 

 spore discharge commences. In exceptional cases, as in that of Stigmatomyces, the 

 walls of certain of the canal-cells (Plate I, fig. 2i,nc) appear to become somewdiat 

 indurated, and to regulate, to some extent, the spore discharge ; but I have observed 

 no other instance than the one just mentioned, unless it be in the case of Sphalero- 

 myces (Plate III, fig. 1) above alluded to. 



