The Development of the Perithecium of 
Polystigma rubrum, DC. 
BY 
V. H. BLACKMAN, Sc.D., F.L.S., 
Professor of Plant Physiology and Pathology , Imperial College of Science and Technology , 
AND 
E. J. WELSFORD, F.L.S., 
Research Assistant , University of Leeds, 
With Plates LXX and LXXI. 
O UR knowledge of the details of ascocarp development in the Pyreno- 
mycetes, when compared with that of other groups of the Asco- 
mycetes, is extremely scanty. Only a few forms have been investigated in 
full cytological detail, such as Aspergilhts ( 7 ), Gnomonia (6), and the forms 
examined by Dangeard ( 3 ). An examination of Polystigma seemed then 
particularly desirable not only on this ground, but also from the fact that the 
earlier investigations of Fisch ( 5 ) in 1882 and Frank (6) in 1883 suggested 
that this form was of particular interest. Their observations indicated the 
existence of well-marked, coiled, multicellular ascogonia with trichogynes, 
and also of spermatia of peculiar form. Furthermore, Frank believed that 
he had obtained evidence of a fusion between spermatium and trichogyne 
indicating the occurrence of a normal sexual process. It seemed then 
possible that a knowledge of the cytology of this form might throw 
considerable light on the general question of the sexuality of the Asco- 
mycetes and of the Lichens in particular, for the problem which apparently 
faces us in the Lichens, that of the fertilization by a spermatium of a 
multicellular ascogonium, has in no case been completely solved. 
With these hopes, which were, however, doomed to disappointment, 
some tentative observations were made as far back as 1905, but material in 
any quantity was not available till 1908. Difficulties in obtaining complete 
stages and in elucidating the behaviour of the complicated ascogonia, 
together with a change of posts, have delayed the completion of the 
work. 
[Annals of Botany, Vol. XXVI. No. CIII. July, 1912.] 
