430 Mr Rattray on the Distribution of 



were cauglit on the submerged slides which were now 

 sunk from the immediate vicinity of the plants to the 

 bottom of the vessels. The spores were also found to 

 accumulate in very great numbers around the margin of the 

 bottom, but their normal heliotropic behaviour towards the 

 light was disturbed by the injection of the currents of air 

 through the aerating apparatus. Permanent slides of the 

 embryo plants were mounted in weak acetic acid on 

 November 1 — twenty-two days after their extravasation 

 from the parent tlialli, and numerous measurements of the 

 progress of growth were made during the period following 

 their emission up till this time (see table, p. 431.) On 

 November 1 the length of some of the embryos reached 

 1*00 mm., with a breadth of frond varying from 0'035 mm. 

 towards the organic base, and in the vicinity of the origin 

 of the rhizoids, to 0'045 mm. in the middle, from which 

 they again tapered very slowly to the apex, which was 

 bluntly rounded. The cells of these embryos have a very 

 well marked and distinct character in different regions of 

 the frond. The apical cell is in all cases plano-convex in 

 outline, resembling either a semicircle or a segment of a 

 sphere somewhat greater than a semicircle. The suc- 

 ceeding cells (twelve to fifteen in number) are bounded by 

 approximately straight walls, where they are in contact 

 with adjoining cells, but bulge somewhat all round the 

 free parts, their length having to their breadth a ratio of 

 about 2 : 3. Towards the base of this series, however, 

 their absolute size increases in most cases very consider- 

 ably, but their relative dimensions remain fairly constant. 

 Bipartition now takes place, the unicellular filament being 

 replaced by a bicellular, which is in turn soon replaced by 

 a quadricellular — divisions of the daughter cells thus pro- 

 duced occurring after an interval occupied by from 3 to 4 

 cell lengths. Still further divisions have taken place at 

 the middle of the young embryo, so that a cylinder of 

 cells which in the same transverse section present con- 

 siderable variability as to length and general outline is 

 produced. Some of the cells of this cylinder are elongated 

 with somewhat acutely rounded extremities, being from 

 three to four times as long as broad, while others lying 

 between these have divided by walls transverse to the 



