FILICINEM. 



4^3 



sometimes elongated leaves. The differences of habit are chiefly due to the greater 

 or less development of one or -other of the branches of the bifurcations. The 

 sporangia are borne in L. Selago in the axils of ordinary foliage-leaves, but usually 

 they are borne in the axils of leaves which are peculiar in shape and colour, and 

 which form terminal spikes on special fertile branches which are frequently curiously 

 modified. 



In Psilotum the stem is thin, much branched, and developed throughout in 

 a bifurcate manner, so that the plant presents the appearance of a straggling 

 shrub. It possesses no true roots, but a number of underground branches dis- 

 charge the functions of roots. The leaves are few, and are but small pointed scales 

 even upon that part of the stem which is above ground. The sporangia are 

 borne three or four together on small, short, lateral shoots of the branches, and 

 do not form a definite fructification. Similar arrangements occur in T?nesipteris, 

 but here the leaves are much larger. With these genera is associated Phyllo- 

 glossujn, a small Australian plant only a few centimetres high, which differs from 

 them considerably. It consists of a stem arising from a small tubej, and bearing 

 at its lower part a rosette of a few long leaves and one or more lateral roots; it 

 is prolonged above this as a thin scape and terminates in a spike of small leaves 

 bearing the sporangia. The plant is propagated by means of adventitious shoots 

 consisting of a tuber with a rudimentary leafless bud : in this respect it resembles 

 our native Ophrydese. 



The development of the vegetative organs is only thus completely known with 

 reference to native Lycopodieae; our knowledge of the other genera is very frag- 

 mentary. We are indebted for the most valuable information to the labours of 

 Hegelmaier, of Leitgeb, and of Nageli. According to Cramer, Pfeffer, and Hegel-^' 

 maier, and this is corroborated by my own observations, the growing end of the stem 

 of Lycopodium does not possess a single apical cell ; this is true also of the leaf and 

 of the root. The growing point of the stem consists of a small-celled primary 

 meristem which does not in all cases present a distinct differentiation of dermatogen 

 and periblem, but there is a distinct axial plerome which extends to close below the 

 apex. In L. Selago the apex is flat, but in L. complaiiatum^ clavatum, annotmum, 

 alpinum, &c., it projects beyond the youngest leaves in the form of a dome. Just as 

 in Phanerogams, the leaves and the rudimentary branches are not developed from 

 single cells of the growing-point, but from groups of cells which include both the 

 superficial and deep layers of the primary tissue. 



The branching of the stem of Lycopodium may be generally described as being 

 dichotomous, although, according to Hegelmaier, the first development of a branch 

 begins in many cases at the side of the growing apex of the stem. In all cases, 

 however, this takes place above the youngest leaves without any reference to their 

 position, and herein it differs from the branching of Phanerogams. According to 

 Cramer two new growing points of equal activity are formed side by side upon the 

 flat apical surface of Z. Selago, and they in turn develope dichotomously, and 

 Hegelmaier found the same to be the case in the vegetative shoots of heterophyllous 

 species (Z. complanalum, chamcecyparissus). In these cases then true dichotomy 

 occurs. On the other hand, the rudiment of the branch appears as a lateral pro- 

 tuberance from the projecting growing point of the vegetative shoots of Z. clavatum 



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