ETTER: POLYEMBRYONY IN POLYPODIACEOUS FERNS 99 
Those that were to be used for histological study were fixed 
in dilute chrom-acetic acid of the following composition, chromic 
acid 1 gram, glacial acetic 4 cc., water 450 cc., for thirty-six 
to forty-two hours, and gradually brought into paraffin with 
chloroform as the solvent. The prothallia were thoroughly 
cleaned of earth and all foreign matter as soon as they had 
reached the grade of 50 per cent alcohol in the dehydrating 
process. At this step to facilitate handling the small prothallia 
were stained in toto in borax carmine. The serial sections, 7-8 » 
thick, were stained on the slide with safranin, gentian violet, 
and orange G, the last stain being dissolved in clove oil. 
Also, during these researches a considerable number of 
prothallia were divided longitudinally through the midrib. 
Gametophytes bearing embryos were selected from ordinary 
cultures, cleaned somewhat, and transferred to moistened Bristol 
board on the stage of a dissecting microscope where, with a very 
sharp scalpel, a clean cut was carefully made through the 
cushion. Those which bore no perceptible embryos from ob- 
servation with a hand-lens were divided on the soil and carefully 
transplanted to sterilized saucers of soil. 
OBSERVATIONS AND RESULTS 
In each of almost nine hundred prothallia fecundated and 
transplanted, one to several spermatozoids were observed to 
enter and pass down the necks of from two to ten archegonia. 
That is, sometimes there were but two archegonia open when 
male plants were placed near the sinus, and again there were a 
number up to a maximum of ten open at that time. 
At the beginning of the work quite a number of prothallia 
were taken from ordinary cultures, imbedded, sectioned, and 
examined, for the simple purpose of becoming acquainted with 
the material, Matteuccia Struthiopteris, to be used in the experi- 
mentation. During this time two and three eggs were observed 
on a single gametophyte, each of which bore several sperm 
nuclei, 
Prothallia which were left on the soil for from five to ten days 
brought the best results. When it was apparent that more than 
one embryo was present on a prothallium, serial sections were 
made to determine definitely the facts in the case. On the 
prothallia of from five to ten days standing it was not always 
