CONNECTION OF THE BUNDLE-Sl'STEMS. 



3°7 



The variety of the vascular system in the large foliar expansions of the Ferns is worthy 

 of observation : here even in a narrow circle of relationship, e.g. in the genera Polypo- 

 dium and Aspidium (in the sense of Mettenius, Fil. hort. Lips.), some species have separate 

 bundles of the most simple arrangement, others reticulate veins ; here also there are 

 found sometimes in one and the same species, sometimes especially in different species, 

 all intermediate forms between the most different types. The number of the bundles 

 •on a given area is always small in Ferns as compared with Angiospermous Phanerogams, 

 but the plan of their distribution, e.g. in Ophioglossum vulgatum and Platycerium, is 

 often the same as in the reticulated leaves of Dicotyledons. 



d. Connection of the bundle-systems of shoots and branches of different order. 



Sect. 93. The bundle-system of the lateral, similar or dissimilar branches of one 

 relatively leading axis is continuous with that of the latter, and inserts itself upon it. 

 The form in which this is brought about depends in the main upon the morpho- 

 logical quality of the leading and lateral axes, the morphological point of origin of 

 the latter, and the course of the bundles within the axes under consideration. Specific 

 peculiarities are found besides in many cases. According to these relations the 

 following summary may be subdivided thus : — 



I. SIMILAR BRANCHES OF LEAFY STEMS. 



1. Normal Branches ^ 



a. Dicotyledons and Gymnosperms with a ring of bundles. 



Sect. 94. The normal branches of the Dicotyledons and Gymnosperms treated 

 in Sect. 61-63 are in the large majority of cases axillary; we shall therefore speak 

 here of these exclusively. There are but few relevant investigations on the rarely 

 occurring extra-axillary branches, some few of which are referred to below. 



The primary bundle-system of the axillary lateral shoots, when it consists of 

 . leaf-traces, shows four main forms of insertion on that of the leading shoot. 



In most cases it unites itself at the point of insertion of the branch into two or a 

 few bundles : these insert themselves, at the node of the leaf which bears the shoot, 

 on those bundles of the trace of the leading shoot which border on the gap of the 

 bundle-ring (gap of the leaf which bears the shoot) formed by the exit of the median 

 bundles of the trace. 



In a second, apparently less numerous series of cases, the two ot few bundles 

 of the base of the branch enter the ring of bundles of the leading shoot, at the node 

 of the leaf which bears the shoot ; they pursue an individual course down to a lower 

 node, and here insert themselves like bundles of the leaf-trace. 



In these two cases the arjangement of the bundles of insertion is always such 

 that there is direct continuity between the pith of the leading and lateral shoots. 



In a third series of cases the bundle-system of the lateral shoot inserts itself 



' In the sense of Sachs, Lehrb. p. 174, 2ncl Eng. ed. p. 171. 

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