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Transactions. 



division of the epibasal half has taken place by a wall which, instead of being 

 inclined to the basal wall, is parallel to it. The uppermost cell thus has 

 almost the appearance of a suspensor, but comparison with other embryos 

 shows that this cannot be its nature. Fig. 44d represents a transverse 

 section of the parent prothallus at the point at which this embryo was 

 borne, and it will be seen that the prothallial tissues protrude here rather 

 more than usual. Possibly the embryo has been stimulated by this to a 

 rapid elongation. In the other two abnormal cases mentioned the arche- 

 gonial neck appears towards the end of each series, so that the sections 

 must be considered more or less obliquely longitudinal. In the case of 

 that shown in figs. 45a. to 45f there seem to be two inclined walls leading 

 off at very slight angles from the basal wall into the epibasal region, and 

 along with this it must be noticed that the embryo is squat in form. It 

 was situated well up the prothallial protuberance which surrounded the 

 foot of a well-grown plant, where the cells, although not compressed, were 



Figs. 46a-46d. — Young embryo in longitudinal section, showing abnormal 



segmentation. X 135. 



yet all much extended in a horizontal direction. I would suggest that the 

 extension of the young embryo in this direction had caused it to repeat 

 the formation of the epibasal inclined wall. In the third of these abnormal 

 cases (figs. 46a to 46d) it will be seen by reading the series from the last 

 section backwards that the first-formed epibasal wall approaches the basal 

 wall and presumably joins it before the section marked A is reached. 

 Here too, then, it is apparent that this wall is inclined at an unusually 

 slight angle, as is also that in the hypobasal region. These were the only 

 abnormally segmented embryos observed. 



C. Initiation of the Shoot Apex. 



An apical cell is set apart comparatively early in one of the epibasal 

 quadrants, and from this the shoot-apex is formed. In my earlier paper 

 I noted that an apical cell was probably already present in the young 

 embryo shown there in figs. 55 and 56, and a re-examination of these 

 sections in the light of my subsequent studies confirms this belief. The 



