394 Transactions. 



The Embryo. 

 A. General Observations. 



From the study of the limited number of embryos described in my 

 former paper T drew the following conclusions. The first wall to be formed 

 in the .zygote, the basal wall, is transverse to the direction of the axis 

 of the archegonium, and separates the embryo into its two main regions, 

 the hypobasal (lower) region wholly giving rise to the foot, and the 

 epibasal wholly to the shoot. There is no suspensor, cotyledon, or root. 

 The superficial cells of the foot develop into haustorial protuberances. The 

 initiation of an apical meristem in the shoot-region was not traced, although, 

 judging from one particular embryo found, a single apical cell had 

 apparently been set apart very early. The position of the second apex of 

 growth in the young plantlet was described. I have since been able to study 

 a much larger number of embryos, although the series is still not quite 

 complete, lacking certain stages as seen in transverse section. The present 

 study confirms my previous conclusions, and makes more clear the main 

 segmentations of the embryo. It also determines the early initiation of 

 tl\e apical meristem in the shoot, as well as that of the latter's secondary 

 apex of growth. 



The majority of the large number of prothalli which I have examined 

 in external appearance apparently bore no embryos at all. On the other 

 hand, a few, and they almost always of the stouter type, showed the 

 presence of several (Plate LXIII, fig. 1). A good number of very young 

 embryos were found showing only the first one or two segmentations, 

 some of the stouter prothalli bearing from two to five of these. In 

 most instances a prothallus did not bear more than one developing 

 embryo, although one or more undeveloped fertilized archegonia 

 might be present. This condition of things may be compared with 

 what I have found in the prothalli of those New Zealand species of 

 Lycopodium which belong to the two large subterranean types. For 

 example, one large prothallus of L. fastigiatum, which conforms to the 

 elavatum type, bore no fewer than eleven young embryos as well as three 

 young plants. This was, of course, an exceptionally large number, but 

 many of the prothalli of L. volubile, L. fastigiatum, and L. scanosum which 

 I have sectioned showed three or four developing embryos, and it is quite 

 usual for these prothalli to be found with two or three well-grown young 

 plantlets attached to them. 



Generally speaking, all stages in embryo development except the very 

 youngest can be detected in external examination. The two general 

 features which make them thus apparent are, firstly, a superficial localized 

 swelling of the prothallial tissue, and, secondly, the presence of an old 

 archegonium neck at the apex of this swelling. These were what one 

 always looked for. In the case of fairly well advanced embryos, which, 

 however, had not as yet ruptured the prothallial tissues, the interior of 

 this swollen region always appeared somewhat darker than the surrounding 

 tissues. 



It may be as well to state at once the most prominent features in the 

 embryo of Tmesipteris. These are, firstly, the basal wall, which can clearly 

 be traced throughout the whole development until the young sporophyte 

 becomes detached (the plantlet usually detaching itself here, leaving its foot 

 embedded in the prothallial tissues) ; secondly, the superficial swelling of 

 the prothallial tissues around the embryo, together with the repeated trans- 

 verse divisions of the large prothallus-cells lying immediately interior to the 



