352 The British Association at Birmingham. 
Dr. O. V. Darbishire described the development of the 
apothecium in the lichen Peltigera. Spermatia are very rare in 
this genus, being confined to a few species and even in these rather 
rare; yet in certain species apothecia are produced in great 
numbers. Fiinfstiick and Baur have investigated Peltigera, and 
without going into nuclear details Baur has described this as a case 
of apogamy. The author has found that the beginning of the 
apothecium occurs among the young marginal hyphae of the 
thallus. Certain cells of the medullary hyphae, which may he 
followed some distance hack into the older parts of the thallus, 
swell up and stain more deeply than the others; they are at first 
uninucleate, hut soon become multinucleate as they increase in 
size. Fusions with neighbouring cells are common, but no trans¬ 
ference of nuclei has been observed. Soon there is a mass of 
closely interwoven cells full of cytoplasm and containing numerous 
nuclei ; no coiled carpogonia can be made out, but taken as a whole 
these darkly stained cells can be seen to form part of a connected 
system of branched hyphae coming from the medulla further back 
and passing into the cortical margin. The multinucleate condition 
is apparently due to simultaneous nuclear divisions in the cells, not 
to any passage of nuclei from cell to cell. When nuclear division 
is still active, long unbranched but multicellular hyphae grow out 
towards the cortex, forcing their way through the latter generally 
at an oblique angle; these, which are from structure and appear¬ 
ance functionless trichogynes, gradually disappear. Certain of the 
larger cells—the “ ascogonia ”—now grow out, and the nuclei 
formed by simultaneous division ( i.e ., female nuclei) pass into the 
ascogenous hyphae, thus formed, in pairs. From these the asci 
appear to derive their first nucleus in the usual way. 
Miss E. M. M. Hume, in a paper on the leptoids of Polytrichum, 
pointed out that these structures do not deserve the name of sieve- 
tubes in any ordinary sense of the word. Their contents differ 
from those of the other living cells in never including starch grains 
or large drops of oil, but each leptoid has a nucleus. They are 
rich in connecting threads, which are in the terminal walls and are 
also abundant in the lateral walls, especially thickly aggregated 
towards the ends of the cells. The threads occasionally show an 
arrangement into definite areas as in sieve-plates, but are more 
frequently quite diffusely scattered ; where such plate-like areas 
occur there is no change in the thickness of the cell-wall. The 
area of the terminal wall is enormously increased by its bag-like 
shape, so that the end of one cell depends into the lumen of the 
next. The connecting threads do not differ in structure from those 
found in the cortical cells, and they do not appear to undergo any 
progressive change into slime strings, with accompanying alteration 
of the surrounding cellulose into callus. Histological arguments in 
favour of the conduction of organised food materials by the leptoids 
must be based upon the elongated shape of the cells, the great 
area of the terminal walls, and the wealth of connecting threads, 
especially aggregated towards the ends of the cells. From direct 
experiment, the conducting function of the leptoids seems, more 
probably, to be confined to albuminous materials and not to be con¬ 
cerned with carbohydrates. The latter are possibly conveyed by the 
hydroids, which probably have not a purely water-conducting function. 
