2 
Davis . — Spore Formation in Derbesia. 
This paper will describe the development and germination of the 
zoospores of Derbesia L amour ouxii (Agardh), Solier, with special reference 
to the structure and behaviour of the nuclei, and the development and 
fate of the blepharoplast. The material was gathered in the spring of 
1904 at Naples, where, at the Zoological Station, I occupied a table of the 
Carnegie Institution. 
The most satisfactory fixation was obtained with a weak chrom- 
osmo-acetic formula as follows : — 1 per cent, chromic acid 25 c.c., 1 per 
cent, acetic acid 10 c.c., 1 per cent, osmic acid 5 c.c., sea water 60 c.c. 
A similar formula, with the omission of osmic acid, was also satisfactory. 
Sections were generally cut 3 /x thick. The best stain proved to be iron- 
alum haematoxylin with Congo red, and haematoxylin alone for the details 
of nuclear structure. It proved somewhat difficult to use safranin and 
gentian violet because of the numerous plastids which take these stains 
with avidity. 
The Habits of the Zoospores. 
The zoospores are formed slowly, and several days may elapse after 
the development of the sporangium before the segmentation of the 
protoplasm begins. The first large crop generally appeared two or three 
days after material of Derbesia was brought into the laboratory and left 
in sea water, after which zoospores continued to be formed for several 
days. Attempts to hasten their development by raising the temperature 
of the water or by diluting it resulted in the death of the plants. 
The zoospores in the Naples material were remarkably variable in 
size and in number, ranging from 30-50 in the smaller sporangia to 
perhaps 200-300 in the larger. They are spherical or oval, and swim 
slowly through the water with the circle of cilia forward (PL I, Fig. 1). 
They contain very large numbers of small disk-shaped chloroplasts dis- 
tributed throughout the protoplast, so that the zoospores are uniformly 
green and the ciliated region is not conspicuously lighter in colour ; 
there are no pigment spots. 
The zoospores come to rest on the region of the protoplast within 
the circle of cilia, and the latter become distributed in a radiating 
arrangement (Fig. 2) over the surface to which the zoospores become 
attached. 
The Development of the Sporangium. 
The sporangia are globular structures arising from the sides of the 
filaments. It must require a number of days for them to reach maturity. 
The contents of the developing sporangium remain connected with the 
parent filament by a broad strand of protoplasm until the structure has 
attained full size (Fig. 3). The strand then becomes narrower by the 
