682 CONCLUSION 



in its simplest forms) : it is habitual, though with occasional exceptions, 

 in Isocfcs and the Ophioglossaceae, and it is seen in many Ferns, and 

 especially in such early types as the Marattiaceae, and Osmundaceae. 

 The whole plant in these cases consists of a single upright radial shoot, 

 and there is reason to believe that this is itself a primitive condition ; 

 such a view accords with the generally primitive character of the plants 

 in which it is seen. It may, however, result also from reduction, as may 

 often be seen in starved seedlings of annual flowering plants. 



But in all the more advanced types, branching of the shoot occurs, 

 resulting in multiplication of shoots, and ramification often of a high 

 order. It is necessary to put this in relation to the simple unbranched 

 state. The terminal dichotomy of the shoot was probably a primitive 

 mode of branching. It is characteristic of those species of Lycopodium 

 and SelagmeUa, which are held as primitive ; (viz. the Selago section of 

 Lycopodium, and in Selaginclla spinulosa) : it is seen occasionally in Isoetes, 

 in the Psilotaceae, and in the Ophioglossaceae as a rare occurrence, also 

 in the Osmundaceae, and in some other Ferns. Gradual transition from 

 the dichotomous to the monopodial branching may be traced by comparison 

 of the more primitive with the more specialised species of Lycopoiliitm 

 and Selaginella, while in some cases the change may be traced through 

 unequal development of the branches of the dichotomy in passing from 

 the earlier to the later branchings of the individual life. 1 This makes it 

 appear probable that the monopodial is a later and derivative mode of 

 branching. 



It is a question what the relation of these terminal branchings of the 

 shoot may be to such lateral branchings as are seen in Eqnisctum, and 

 Sphenophyllum, or in those Ferns where axillary branching occurs. It seems 

 not improbable that these are in origin quite distinct modes of amplification 

 of the vegetative system from those brought about by terminal branching, 

 and that they are to be regarded rather as regularly recurring and early, but 

 nevertheless accessory developments. A reason for this distinction is to be 

 found in what is seen in Equisetum, for here terminal fissions of the strobilus 

 are occasionally to be found, and are quite different in nature and origin from 

 the formation of branches normal for the genus. Again, in the Ophioglos- 

 saceae, in which family dichotomous branching has been seen as a rare 

 occurrence, and in many Ferns such as Pteris, which show occasional 

 dichotomy, buds arise at points remote from the apex of the shoot, in the 

 former case upon the roots, in the latter commonly near to the bases of the 

 leaves : these are clearly adventitious. All of these are probably of distinct origin 

 and nature from the terminal branching which is fundamentally dichotomous. 

 Moreover there is a structural difference between terminal ramifications and 

 branchings which are accessory : the former carry on the vegetative con- 

 struction with amplified stele, and fully formed leaves arranged as in the 



'This is l.clirvcd by Bruclimann to l>c the rule throughout the genus Sc/aghu-l/a, 

 their first branching being regularly dicliotomous. /,.<'., p. 18. 



