On the Morphology and Development of Phoma Richardiae n. sp. 
249 
this process it is impossible to see; but it appears to be usually small. 
A number ot vegetative hyphae may also arise from the developing mass 
{Fig. 1. ij, 18, 20 ). The primordium becomes eventually more or less 
spherical or oval. 
It is sometimes formed from two hyphae lying close together 
(Fig. 1, 2 i). 
This method of development is commoner on some media than 
others. On plum agar it is rare; on Salep agar, and on 5% Gelatine 
containing 5 °/ 0 Cane Sugar, however, a considerable number of pycnidia 
arise in this manner. Pycnidia so formed are notable for their small size 
— they are rarely more than 50 ja in diameter — and their regularity 
of outline. 
An extreme case of this method of formation was observed where 
a great number of spores were brought on to a hanging drop of weak 
potato-decoction gelatine. While a great number of the spores behaved 
in a manner to be subsequently described, some swelled, and, after pro¬ 
ducing one or more short tubes, divided repeatedly to form a spherical 
mass of tissue from which a minute pycnidium was eventually evolved 
(Fig. 1. — 26). During growth a great deal of oil was secreted, and it was 
sometimes necessary to place the cover slip in Xylol before the structure 
of the mass could be seen. Sometimes it appeared as though more than 
one spore contributed to the formation of the primordium (Fig. 1 , 2 j, 24 ). 
Intermediate methods of formation are common on all media. In¬ 
deed, a more or less regular sequence is to be observed in the method 
of pycnidia formation in a Salep agar culture. The first formed originate 
through the branching and interweaving of several hyphae (Fig. 1, 12 — 14 ), 
then follow a great number produced around a single hypha (or two 
hyphae lying close together) by profuse branching of a few adjoining 
cells, the branches applying themselves closely to the main strand, and 
the latter itself dividing to a varying extent (Fig. 1, 27 — 29 ). Later on 
the primordium is produced mainly by the repeated division of a few 
cells of one hypha, comparatively few branches assisting (Fig. 1, 18 — 20 ). 
It is tolerably certain that pycnidia may, finally, be produced solely by 
the repeated division of contiguous cells, no branches whatever arising 
therefrom. In development, however, the mass becomes so complex that 
it is impossible to say whether some of the cells have arisen by bran¬ 
ching, or by division; though cases are met with (Fig. 1, 16), which 
present every appearance of having been developed solely by the latter 
process. 
In order to observe the changes going on after the cellular mass 
becomes too complex to see through, cultures were allowed to grow for 
four or five days in a PETRi-dish on plum agar; pieces of different ages 
were then cut out, killed and fixed in chromacetic '), and embedded in 
paraffin in the usual way for microtoming. The agar hardened sufficiently 
to allow of fairly good ribbons 1 and 2 /u thick being cut. Some diffi¬ 
culty was met with in the selection of a suitable stain, aß it was necessary 
to have the cell walls clearly differentiated. Con go-red, followed by 
Gentian-Violet was eventually used. Congo-red, even in concentrated 
solution stained the walls too faintly to be satisfactory alone. 
1) 3 g Chromic acid, 1 ccm Glacial Acetic acid, 99 ccm Water. 
