TRANSACTIONS OF SECTION K. 689 
The ascocarp originates as a tangle of septate hyphae among which sexual 
organs are not differentiated. Normal fertilisation is replaced by the fusion of 
vegetative nuclei in pairs, occasionally preceded by migration. The process is 
quite analogous to that which takes place in ‘ pseudapogamous’ fern prothallia,' 
and probably also in certain Uredinew,’ and in the Basidiomycetes. Cells containing 
fusion-nuclei give rise to sporophytic or ascogenous hyphw; those in which fusion 
has not taken place produce the paraphyses and other gametophytic structures. 
Divisions in the sporophytic hyphae show sixteen chromosomes. Asciare formed in 
the usual way, but since the terminal cell continues its growth, they are regarded 
as lateral branches of the ascogenous hyphe. 
After it is cut off, the two nuclei of the ascus enter independently on the 
prophases of a heterotype division. They fuse soon after the stage of the first 
contraction. Fusion is regarded as brought about by their close proximity at a 
time when the nuclear membrane is breaking down ; occasionally it fails to take 
place. The subsequent stages of the first and second mitoses in the ascus are in 
agreement with those described by Farmer and Moore (1905) for the reducing 
divisions of various animals and plants; the chromosomes divide ¢ransversely in 
the heterotype. 
The chromosomes throughout the meiotic phase are sixteen in number; but 
since sixteen is the diplocytic number and, at this stage, the reduced number is 
typically present, they are regarded as representing two gametophytic sets of 
chromosomes, Fusion in the ascus thus results in the doubling of the chromo- 
somes. 
In. the prophase of the third division sixteen chromosomes appear; they 
separate without fusion, so that only eight pass to each daughter nucleus. 
second reduction is thus brought about, and the true gametophytic number of 
chromosomes is restored. Probably the extraordinary regularity with which two 
fusions occur in the life history of the Ascomycetes is due to the establishment of 
two reductions in the ascus. 
In all investigated organisms the meiotic phase is related to fertilisation or its 
equivalent ; the simpler reduction of the third division is held to be connected with 
the fusion in the ascus. It is probable that a reduction of this type compensates 
other asexual fusions also. 
A method of distinguishing between sexual and asexual fusions is thus 
suggested. 
The processes in the ascus of H. rutilans are related to those observed in 
Phyliactinia* and the few other Ascomycetes studied from this point of view. 
There is reason to believe that a sorting of the chromosomes, analogous to that 
seen in meiosis, takes place in the third division of the ascus; the most essential 
difference between the two reductions seems thus to lie in the more complex 
prophases of the heterotype division and particularly in the characteristic con- 
traction of the chromatin. 
Spore formation was also studied; the general appearance was that described 
by Harper, but neighbouring vacuoles take part in the process. 
The main observations on H. rwtilans and especially those relating to the third 
division in the ascus have been confirmed by the author in conjunction with Miss 
HK, J. Welsford for Peziza aurantia. 
4, Enzymes: their Mode of Action and Functions. 
By Professor H. E. Armsrrone, £.2.8., and Dr. E. F, ARMSTRONG. 
Joint Discussion with Sections D and L on the Teaching of Biology in 
Schools.—See p. 547. 
1 Farmer and Digby, 1907 2 Blackman and Fraser, 1906 ® Harper, 19065. 
1907. YY 
