MINUTE STRUCTURE OF PLANT HYBRIDS. 



219 



the male element or fertilising cell of the pollen grain and the female element or egg-cell 1 

 of the ovule have equally contributed to the rearing of the hybrid organism. 



But to quit now our consideration of Philageria as a hybrid, it may possibly 

 possess an interest in the future from the standpoint of species evolution. That Philesia 

 and Lapageria are closely-related forms cannot well be doubted from what we have 

 already seen of their histological details. The older botanists, guided only by naked-eye 

 characters, considered that the parents well deserved to be rauked as genera. The latest 

 advocate of this view was Sir William Hooker, but his distinguished son, Sir Joseph 

 Hooker, thus expresses himself in his Flora Antarctica : — " With regard to the genus 

 Lapageria, it is so closely allied to Philesia that I doubt its validity, the chief differences 

 being the nearly equally-divided perianth of Lapageria, its more distinctly three-lobed 

 stigma, oblong berry, twining branches, and differently nerved leaves, in all which respects 

 it is more evidently a genus of Smilacece than either Callixene or Philesia." Now, in 

 all of these features, except the twining nature of the stems, I have noticed examples of 

 Lapageria which tend to break down the generic distinctions. 



Thus the nearly equally-divided perianth in Lapageria is not invariable nor is the 

 fusion of stamens, while the figures of leaf- venation prove that both are fundamentally the 

 same. Therefore we believe that the differences in the parents may largely be explained 

 as modifications on some original common type brought about to suit the greatly altered 

 environmental conditions. Here I may be allowed to quote the opinion of the late John 

 Ball, F.R.S. : # — " The true explanation, in my opinion, of the exceptional poverty of the 

 Patagonian flora is to be sought in the direction long ago indicated by Charles Darwin, 

 when, in discussing the absence of tree-vegetation from the Pampas, he remarks that in 

 that region, recently raised from the sea, trees are absent, not because they cannot grow 

 and thrive, but because the only country from which they could have been derived — 

 tropical and subtropical South America — could not supply species organised to suit the 

 soil and climate. So it happened in Patagonia — raised from the sea during the latest 

 geological period, and bounded to the west by a great mountain range mainly clothed 

 with an Alpine flora requiring the protection of snow in winter, and to the north by a 

 warm temperate region whose flora is mainly of modified subtropical origin — the only 

 plants that could occupy the newly-formed region were the comparatively few species, 

 which, though developed under very different conditions, were sufficiently tolerant of 

 change to adapt themselves to the new environment. The flora is poor, not because the 

 land cannot support a richer one, but because the only regions from which a large popu- 

 lation could be derived are inhabited by races unfit for emigration. The rapidity with 

 which many introduced species have spread in this part of South America is, perhaps, to 

 be accounted for less by any special fitness of the immigrant species than by the fact that 

 the ground is to a great extent unoccupied. Doubtless, if no such interference had taken 

 place, and the operation were left to the slow action of natural causes, a gradual increase 

 in the vegetable population would come about. Fresh species of Andean plants would 



* Jour. Linn. Soc, vol. xxi. p. 207. 

 VOL. XXXVII. PART I. (NO. 14). ^ 2 K 



Lapageria 

 rosea. 



2. Philageria 

 Veitchii. 



3. Philesia buxi- 



folia. 



