28 Transactions. 



which the new apex of growth could be seen. In longitudinal section it was 

 seen that the rounded protuberance at the base of the plant shown in 

 fig. 68 was formed by a surface group of actively dividing meristematic 

 cells (a single apical initial could not be traced), and that from this 

 meristem a plerome strand connecting with the central strand of the plant 

 was in process of formation (fig. 63). Also it was seen that two tracheides 

 were leading out from the centre of the plant-axis towards the new apex. 

 Thus we may say that the development of the new axis of growth is 

 adventitious, and may compare it with the well-known adventitious origin 

 in the epidermal and outer cortical cells of older rhizomes of groups of 

 meristematic cells which are frequently to be observed either in a state 

 of arrested development or about to develop into lateral buds. It must, 

 however, be noted that whereas these lateral buds are not confined to any 

 part of the rhizome, but appear in a quite haphazard manner, the secondary 

 apex of growth in the young plantlet is always differentiated in the one 

 position. Thus there is no root to be distinguished in the young plant 

 of Tmesipteris, there being developed, both above and below the original 

 foot, a rhizome identical in the two cases in appearance, function, and 

 manner of growth. 



A series of transverse sections through the foot of a young plant which 

 consists of both primary and secondary rhizome portions — such, for example, 

 as that given in fig. 72- — shows that there is a continuous vascular strand 

 throughout the whole rhizome, identical in structure in the two portions 

 of the rhizome, and unbroken in the foot region. Before the secondary 

 apex of growth is differentiated in the young plant the vascular strand 

 inclines bodily into the foot. When the new apex is formed a plerome 

 strand is differentiated from it, and it would appear that this joins on 

 with the primary strand at the angle where the latter inclines into the 

 foot. Possibly the first vascular elements in this secondary strand are 

 actually formed from the angle of the primary strand in connection with 

 the transport of food from the prothallus to the new apex. In fig. 63 

 is shown the stage at which the plerome strand of the secondary portion 

 of the rhizome is in its earliest development, but vascular elements seem 

 to be leading out to meet it from the point where the strand of the 

 primary part of the rhizome leads down into the foot. 



The growing apices of the young developing plantlets are whitish-grey 

 in colour and more translucent than the rest of the rhizome, and are often 

 slightly swollen. In this respect, and in the general appearance of the 

 young rhizome, there is a certain similarity between detached portions 

 of prothalli and of young plants. The fungal coils are present in the 

 cortical cells of young plants which are still attached to their prothalli, 

 but apparently the fungus does not spread from the prothallus to the 

 plant, but the latter is early infected through its rhizoids. Several of the 

 young rhizomes bore short swollen lateral shoots (fig. 72), clear or almost 

 light-green in colour, and one frequently noticed on the rhizomes of both 

 young and older plants points of meristematic activity. Besides this adven- 

 titious method of branching, the rhizome-apex may fork dichotomously 

 (fig. 75). Sooner or later one or other of the main ends of the young 

 rhizome grows upwards as an erect aerial shoot, losing its rhizoids and 

 decreasing in thickness in the transition region. The aerial shoot is at 

 first whitish in colour and is quite devoid of both rhizoids and scale leaves, 

 but at length its apex becomes green and gives rise to the first scale leaves 

 (figs. 5, 73, 74). After a few of these scale leaves have been formed, 



