312 PRIMARV ARRANGE.MEXT OF TISSUES. 



In the node of Potamogeton natans the bundle-system of the young axillary shoot 

 coalesces so as to form a single bundle, which inserts itself on the median bundle of 

 the leaf which bears it, at the point where it curves outwards. The other investigated 

 Potamogetons — P. lucens, gramineus, pectinatus, and pusillus — show a quite similar 

 insertion, with the difference that the bundle which comes from the axillary shoot is 

 not inserted on the bundle passing into the leaf which bears it, but on the axile 

 sympodial bundle which passes downwards at the node. Comp. Fig. 123, p. 273. 



As far as is known, the naturally very simple relations of insertion in those 

 Phanerogams which have an axile bundle resemble those in the last-named Mono- 

 cotyledons. 



r. Feni-J ike plants. 



Sfxt. 96. Among the Filicinese there is sometimes forked, sometimes Mono- 

 podial branching; in many species, as in Aspidium Filix mas, Athyrium Filix foemina, 

 both forms of branching are found side by side. 



INIonopodial branching occurs undoubtedly in the Salvim'acecB, Marsiliacece, and 

 in many Filices. Very many Filices show a shoot-system, apparently composed of a 

 main axis and lateral shoots, in respect of which it is a matter of controversy whether 

 it is a IMonopodium, or a Sympodium composed of unequally developed successive 

 forks. It will here be treated as a Monopodium, in accordance with the conclusion 

 of iNIettenius. But I remark distinctly that I only accept this conclusion in order to 

 simplify the description hei-e to be given, and that I leave the controversy in question 

 quite undecided. The fact that the insertion of the bundles of the actual lateral 

 shoots appears in many cases in point to support the conclusion of Mettenius 

 cannot by any means decide the question, since unequally strong growth of originally 

 equivalent shoots may also have as its result an originally unequal arrangement of 

 their vascular bundle-system. 



The normal lateral shoots of the plants of this series, with the exception of 

 many Hymenophyllums and Davallias, which in this point also are the subject of 

 controversy, are not axillary, nor have they even any other constant relation to the 

 insertions of the leaves. 



They arise either from the stem, and sometimes close to the point of insertion 

 of the leaf, laterally or at the back of the latter, sometimes at a great distance from it, 

 between two leaves ; or they arise on the back or sides of the base of the petiole 

 itself, often, as in the ordinary branchings of Aspidium Filix mas, which may be 

 accordingly considered as belonging here, at a considerable distance from the point 

 of insertion, in the above-named example about 2-3 centimetres from it. Comp. 

 Fig. 132, C, p. 286. 



In the undoubtedly Monopodial branching of many Filices with more than two 

 rows of leaves, the vascular bundle-system of the lateral shool is united as a rule 

 towards the point of origin to one thin and not hollow bundle, which is inserted on 

 one bundle of the main axis. This is the case in the lateral shoots of Aspidium 

 cristatum, spinulosum, Blechnum Spicant, Athyrium Filix foemina, Polypodium al- 

 pestre, Alsophila aculeata, &c.^, which appear at or below the back of the base of the 



' llofraeibter, Beitr. l.(. — Stenzel, I.e.; comimre p. 283. 



