666 TRANSACTIONS OF SECTION K. 
visionally, the name Zygopteris Pettycurensis, exhibits a distinct protostele, 
and thus occupies the same position in the Zygopterid alliance that 
Thamnopteris Schlechtendalii does in the Osmundaceous. 
The stem of this new species is circular in transverse section. The wood 
of the stele consists of an inner zone of short, square-ended, reticulately 
thickened tracheides, and an outer zone of long, pointed, reticulate 
tracheides, while the protoxylem groups have scalariform thickenings on 
their walls. 
Petioles are given off at long intervals. The petiole trace is elliptical 
in shape, with a deeply sunk protoxylem group at each end. Islands of 
parenchyma develop round each of these groups and increase until the trace 
is broken through at both ends. The trace thus assumes the typical 
H-shape of the Zygopterid bundle. 
The roots come off irregularly and also have two sunken protoxylem 
groups. The stem branches frequently and in this resembles Z. corrugata 
(Will). 
Starting with Z. Pettycwrensis a series can be established among the 
Zygopteridese, which is exactly parallel to that lately shown among the 
fossil Osmundacew. The development in the former group, however, was 
completed before that in the latter group began, for the Zygopterid series 
began in the Calciferous Sandstone series, as far as we know, and ended in 
the Permo-Carboniferous, while the Osmundaceous series began in the 
Upper Permian and continued on to Tertiary times. 
5. The Number of Bacteria in the Air of Winnipeg. 
By Professor A. H. Reainatp BunuEr, Ph.D., and Cuas. W. Lown. 
The authors determined the number of bacteria, mould spores, and 
yeast cells present in the air upon the campus of the University of 
Manitoba. The observations were made each week throughout a whole 
year. Both the volumetric and the plate methods were employed. The 
volumetric method was practically fhe same as that used by Professor 
Percy Frankland in London in 1886. Curves were plotted showing the 
number of micro-organisms present in 10 litres of air, and also the number 
falling upon a square foot of horizontal surface each minute. 
The investigation showed that the maximum number of micro- 
organisms—namely, 263 in 10 litres of air—occurred on September 28. 
During the six months November to April inclusive the average number 
in 10 litres of air was 0°9. It was therefore found that during the winter 
half of the year the air of Winnipeg is remarkably free from micro- 
organisms. During two successive weeks in January only two colonies were 
developed from 100 litres of air in each experiment. The average number 
of micro-organisms during the summer half of the year, May to October 
inclusive, was 10°33 in 10 litres. ‘The authors discussed the effects of 
temperature, rain and snow, wind, and other conditions upon the experi- 
mental results. 
The number of micro-organisms falling upon a square foot of surface 
during a minute was found to vary from three in winter to 8,500 on a very 
windy day in summer. 
6. Some Problems connected with the Life History of Trichodiscus 
elegans, Welsford, n.gen. n.s. By Miss EK. J. WELSFoRD. 
The vegetative filaments of Trichodiscus elegans are multicellular and 
cohere to form a flat pseudo-parenchymatous disc; the free ends of the 
filaments protrude laterally and bear scattered multicellular hairs ; the older 
