2 16 Margaret Hume. 
all branches upon which the pycnidia and apothecia of Derniatella 
are observed should be cut off some distance below the most 
proximal positions of the fructifications and burnt. The fungus 
spreads slowly, hence pruning of the kind suggested should check it 
effectively. 
Summary. 
The results so far obtained may be thus summarised :— 
(1). Dermatella prunastri Pers. has been grown in pure culture 
from conidia and from ascospores. (2). The mycelia arising from 
both these kinds of spores when growing on nutrient agar and 
sterilised pieces of greengage wood and bark produced pycnidia 
after some three weeks’ growth. (3). The mycelium was found 
present in all the tissues of the host and particularly in the wood 
and pith. (4). The vessels, tracheids, and fibres are not delignified 
and the hyphae pass from one cell to another by way of the pits. 
(5.) The mycelium advancing up a branch is preceded by gumming 
in the woody elements. (6). The inoculations of healthy greengage 
trees with the mycelium of Derniatella prunastri led to infection. 
ON THE PRESENCE OP CONNECTING THREADS 
IN GRAFT HYBRIDS. 
By Margaret Hume, 
Late Bathurst Student of Newnham College, Cambridge. 
[With One Figure in the Text.] 
Historical. 
I ^HE genesis of connecting threads has long been a subject of 
discussion and it still remains an open question whether they 
arise from the spindle-fibres and perforate the cell-wall ab initio or 
whether they may be formed subsequently. The possibility that 
both methods occur, of course, is not excluded. 
It was Tangl (14, p. 182) who first noticed that the connecting 
threads between the cells of certain endosperms resemble very 
strongly the striations which connect the endosperm nuclei during 
their division in the embryo-sac and hence arose the view that 
connecting threads originate as spindle-fibres and perforate the 
cell-wall from the time of its origin, a view shared by Russow (12, 
