THE LEAF. 



239 



reiterated, according to which the stem of all vascular 

 plants is built up of a number of shoot-segments 

 (phytons) and is in reality a sympodium in the sense 

 that each leaf represents the termination of the stem, 

 each new shoot-segment sprouting from it in a lateral 

 position in the same way precisely as the young stem 

 of Jhmchs, for example, is at first constituted.* It 

 follows from this view that (with the exception of 

 those foliar organs which have been secondarily derived 

 from division of a single organ) the leaves of a shoot 

 are primitively terminal structures and the lateral 

 position is a purely secondary one. 



Besides J uncus, we have, as Velenovsky points out, in 

 Dicotyledons which in other respects exhibit Mono- 

 cotyledonous features, viz., Piper and Peperomia, an 

 instance in which the youngest stage of the seedling 

 shows a complete absence of any stem, the first two or 

 three foliage-leaves sprouting out of one another 

 laterally, and at a point, in each case, some wiay 

 above the base of the leaf-stalk. These actual facts of 

 seedling organization refute the modern view that an 

 axis is present at every stage of life, and that leaves 

 are lateral appendages thereof. But this view may 

 also be shown to be improbable by the following 

 argument. If the Monocotyledonous structure has 

 been derived by reduction from the Dicotyledonous 

 type, a theory which is entirely bound up with the 

 view that the stem is a primeval feature, then the 

 completely stem-less organization of the seedlings of 

 Juncus and Piperacea3 must be regarded as having 

 been derived from that in which a stem is present, a 

 view which, unless the phy ton -theory be admitted, 

 is obviously absurd, inasmuch as it involves the 

 recognition of the phy tonic structure in these plants, 

 for, apart from the phyton-theory it cannot be imagined 

 that at one end of the scale of development a stem 



* The facts of embryogeny in Bryophytes, Pteridophytes, and Phanero- 

 gams are essentially similar in all these groups, and support the view that 

 the sporogonium is the primitive ancestor of the leaf, arising as it does from 

 the same quadrants ; hence the leaf is originally a terminal structure. 



