286 Transactions. 



large size, and consists of a uniform parenchymatous tissue bounded 

 where it is in contact with the tissues of the prothallus by a distinct 

 epithelium. In view of Miss Wigglesworth's statement (18) that in 

 L. complanatum a short strand of vascular tissues passes from the main 

 stele into the foot, I carefully examined transverse sections of the foot 

 in several plantlets of different stages of growth of the present three 

 species. In the case of L. voluhile my results bear out very closely Miss 

 Wigglesworth's statements. In the smaller plantlets of this species a 

 strand of small thin-Avalled cells with abundant cell-contents penetrates 

 well into the centre of the foot. It is in connection with the vascular 

 tissues of the main stele. In older plantlets a few tracheides make their 

 appearance in this strand. In one case, in the sections nearest to the 

 main stele, these tracheides were in two groups separated by a single 

 group of thin-walled cells, while towards the centre of the foot they 

 gradually disappeared till there was only one left, much in the same 

 manner as described by Miss Wigglesworth in the case of L. complanatum. 

 In these larger plantlets the sclerenchyma in the foot closed in the vascular 

 tissues together. In the young plants of L. scariosum and L. fasti- 

 giatum that I examined there is very little development of vascular tissues 

 from the main stele into the foot. In the former species the, foot is 

 vary large, but only in the sections nearest to the main stele was any 

 small-celled tissue seen to lead off from the stele into the foot, and no 

 tracheides were present. In L. fastigiatum the foot-strand was slightly 

 more developed, but not to the same extent as in L. voluhile. In all 

 three species the epithelial cells of the foot remain intact even on the 

 largest plantlets, but the outer walls of the cells become strongly thickened. 

 The prothalli of these species belong to one or other of the large sub- 

 terranean types, and they continue to grow in size in many cases 

 long after the young plant has begun to develop. The development 

 of vascular tissue in the foot of the young plant varies in extent in 

 different individuals of the same species, and possibly this is dependent 

 simply upon the size to which the parent prothalli grow. There is no 

 indication of a SAvelling comparable in any way with the protocorm of 

 L. cernuum. The young plants take their origin from the upper region 

 of the prothallus, in the case of L. voluhile and L. fastigiatum generally 

 at one end or the other of the main groove or depression which is pre- 

 sent upon the upper surface of the prothallus, and in the case of 

 L. scariosum at some point or other on the margin of the upper bulging 

 region. In each case the first root shows as a peg-like outgrowth 

 at the base of the young stem. The stems are cylindrical, colour- 

 less, and naked (except for a few minute scale-like leaves) for a 

 greater or lesser length according to the depth of the prothallus 

 below the surface of the ground. In L. scariosum, whose prothalli 

 are the most deeply buried, the stems may be as much as 2-3 in. 

 in length before the ordinary assimilating leaves are formed. Young 

 plants of each of these species are figured on the prothalli which have 

 been referred to in Section III of this paper. The relative positions 

 of the foot, stem, first leaf, and first-root rudiments in the young plant 

 of L. fastigiatum are shown in fig. 84. This is a model of a developing 

 embryo of this species viewed from above. It is tilted slightly in order 

 to show the full sweej) of the large foot and the projecting first root. In 

 this case the apex of the stem and first leaf had just emerged from 

 the tissues of the prothallus, but the root would not be apparent 

 externally. 



