708 TRANSACTIONS OF SECTION K 



admittedly independent developments, exhibit an essential correspondence 

 amounting to a homology of organisation. The resemblances are not analogies, 

 for it is doubtful whether the ' leaves ' in the different cases correspond in 

 function. The comparison of the shoot of the sporojDhyte of a Vascular Cryptogam 

 with, for example, the shoot of the Moss seems equally justifiable. It is only 

 forbidden by strict phyletic morphology, which for our purpose has no juris- 

 diction. The general agreement as regards the leaf- arrangement between the 

 Ferns and the Bryophyta suggests that similar laws will be found to hold in 

 the shoot of both gametophyte and sporophyte. Apart from plagiotropic shoots, 

 there is a constructionally dorsiventral type of fern-rhizome. The leaves of this 

 alternate as in the leafy Liverworts, while the radial type of fern corresponds 

 to the moss-shoot. It is significant that the early leaves of radially constructed 

 ferns usually exhibit a divergence of i in the seedling, passing higher up the 

 stem into more complicated arrangements, and the same is the case in mosses. 

 I must not enter into questions of phyllotaxy, but may remark on the hopeful- 

 ness of attacking it from the study of the simpler shoots of Algae and Bryophyta 

 rather than, as has usually been done, beginning with the Flowering Plants. 



In some ferns (the striking example being C'eratoplcris) the relation between 

 the segmentation of the apical cell and leaf-production is as definite as in the 

 moss, each segment giving rise to a leaf. This may hold more widely for 

 ferns than is at present demonstrated, and the question deserves thoroug'h re- 

 investigation to ascertain the facts independently of any theoretical views. 

 That the coincidence of the segmentation of the shoot expressed by the leaf- 

 arrangement a)id the segmentation of an apical cell is not a necessary one is, 

 however, clearly shown in other ferns, and is obvious in the case of shoots 

 with a small-celled meristem. The two segmentations ap|)ear to be determined 

 by some deeper system of relations, which may also be manifested in a coenocytic 

 plant-body. 



In the complication of the uniaxial shoot introduced by branching also there 

 seems to be an advantage in a wide area of comparison. The question most 

 often discussed concerns dichotomous and monopodial branching. If the details 

 of development are to be taken into consideration, the term 'dichotomy' has 

 usually been very loosely applied. Apparent dichotomy, the continuation of 

 one shoot by two equally strong ones, is fairly common. But in most cases 

 investigated in detail the branching seems to be really monopodial and the 

 forking due to the equally strong development of a lateral branch close to the 

 main apex, not to the division of the latter. In plants growing by a single initial 

 cell almost the only case of strict dichotomy known i.s the classic one of Dictyota. 

 The branching of the ferns has been the subject of nmnerous investigations, 

 but there is a great lack of developmental data. ITsually the branches stand 

 in some definite relation to the leaves of the shoot, behind, to one side or on 

 the leaf-base itself, the most interesting but least common case being when the 

 branch is in an axillary position. When the mature shoot only is considered, 

 it is possible to argue for the derivation of monopodial branching from dichotomv 

 or the converse. Even the facts obtainable from the mature plant, however, 

 point to the dichotomous branching being a modification of the monopodial, the 

 opposite view appearing to land us in difficulties regarding the morphology of 

 the main shoot. '=_ It is unlikely that a dichotomy involving the division of* the 

 apical cell occurs in the fern-shoot, and comparison with the Bryophyta confirms 

 the suspicion that the cases of dichotomy are only apparent. 



In considering the construction of the shoot w-e are at present limited to 

 comparison of the normal structure and development. The system of relations in 

 the .shoot of the fern, affecting in the first place the distribution of the leaves 

 and secondly that of the branches, appears, however, to be of the same nature 

 as hi the independently evolved shoots of Bryophyta and Algfe. A morpho- 

 logical analysis based on the simpler examples may "lead on to the experimental 

 investigation of the common construction. The relation that exists between 

 the general construction and the vascular anatomy offers a special and more 



'= The conclusion arrived at by Schoute, that the angular leaf in ' dicho- 

 tomous ' branching and the subtendino- leaf in monopodial branching are 

 equivalent, supports this view. Fecueil des Travanx bofaniques Nierlandais, 

 vol. xi. 



