Holloway. — Prothallus, &c, of Tmesipteris. 395 



foot (the browned " cup " being an outstanding feature on the prothallus- 

 surface at an old point of attachment of a plantlet) ; thirdly, the haustorial 

 protuberances from the foot into the tissues of the prothallus ; fourthly, 

 the presence of a single large apical cell in the outer, or shoot, region, in 

 some cases a second apical cell being set apart in the other outer quadrant ; 

 and, lastly, the Tmesipteris embryo, when compared with those of other 

 Pteridophytes, shows the important feature of the absence of suspensor, 

 cotyledon, and root organs. 



The hypobasal region of the very young embryo curves somewhat as 

 it develops, so that frequently a single longitudinal section does not 

 show both foot and shoot cut truly medianly. On this account, in illus- 

 trating some of the embryos on which my description is based, I have 

 thought it advisable to show a series of several consecutive sections. 

 Unless otherwise indicated, a series so illustrated always consists of con- 

 secutive sections. Again, in the epibasal region the apical cell never seems 

 to be in the line of the archegonium-axis, so that the young shoot-apex 

 bursts out from the tissues of the prothallus inclined at a greater or less 

 angle, which, moreover, is not infrequently out of the plane in which the 

 prothallus-limb lies. Hence in longitudinal section the apical cell is some- 

 times cut slightly obliquely. 



In several cases developing embryos were seen on sectioning to be 

 browned, the nuclei being small and the cell-walls more or less distorted. 

 This would seem to have been due not to anything in the preparation of the 

 material for embedding in paraffin, but to the previous death of the embryo. 



B. First Segmentations. 



In my earlier paper I described and figured several very young embryos 

 (7, figs. 52 to 57), noting (p. 22) that the first wall to be formed divides the 

 embryo into lower and upper regions, and that the next division is in 

 the hypobasal cell by a wall leading at an angle from the basal wall into 

 the lower end. The exact sequence of the subsequent segmentations was 

 not demonstrated, although from the figures and from the further study of 

 the same embryos it would appear that an inclined wall is formed also in 

 the epibasal cell, the embryo thus attaining a quadrant stage. From the 

 present study, also, this seems to be the normal sequence of segmentation, 

 although several abnormal cases will be described. 



28 29 



Figs. 28a, 28b, 29. — -Two fertilized egg-cells in longitudinal section. X 100. 



The fertilized egg-cell at once grows considerably in size. A good many 

 instances of this condition were observed, two of which are shown in 

 longitudinal section in figs. 28a, 28b, and 29. The former of these was cut 

 a little obliquely, but from fig. 28a it is apparent that cell-divisions in the 

 surrounding prothallial tissue begin immediately. A considerable number 

 of embryos showing the first segmentation only were found (figs. 30 to 

 34 A-c. The basal wall is always transverse, and divides the fertilized egg 



