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XIV. — A Comparison of the Minute Structure of Plant Hybrids with that of their 

 Parents, and its Bearing on Biological Problems. By J. Muirhead Macfarlane, 

 D.Sc, F.R.S.E. (Plates I.-VIII.) 



(Bead 4 th May and 15th June 1891.) 



I. Introduction, 



II. 



Comparison of Hybrid Structure "with 

 that of the Parents — 



(a) Philageria Veitchii, 



(b) Dianthus Grievei, 



(c) Geum intermedium, 



(d) Bibes Gulverwelli, 



(e) Saxifraga Andrewsii, 

 (/) Erica Watsoni, . 

 (g) Bryanthus erectus, 

 (h) Masdevallia Chelsoni, 

 (i) Cypripedium Leeanum. 

 (k) General Observations, 



III. Comparison of the Colour, Chemical 



Constitution, Odour, Flowering Period, 

 and Constitutional Vigour of Hybrids, 

 with those of the parents, . 



IV. History and Structure of Cytisus 



Adami, 



V. General Summary of Results on Seed 

 Hybrids, 



PAGE 



203 



207 

 220 

 225 

 229 

 232 

 237 

 238 

 242 

 245 

 249 



254 

 259 

 270 



FAGE 



VL The Bearing of Hybridity on Biological 

 Problems — 

 (a) Relative Potency of the Male and 

 Female Sex Elements in the Forma- 

 tion of an Organism, . . . 272 

 (6) Unisexual Heredity, .... 273 



(c) Bisexual Heredity, .... 274 



(d) On the Divergence of some Hybrids, " * 



or Parts of Hybrids, towards one 

 Parent, 275 



^e) Mechanical or Physiological Obstacles 

 to Fertilisation as an Explanation 

 of Infertility in some Hybrids, . 276 



</) The Relative Fertility of Hybrids in 



Relation to Heredity, . . . 277 



iff) Vegetable Cell Structure in Relation 



to Hybridity 278 



(h) Value of Microscopic Characters in 

 the Future Verification of Doubtful 

 Hybrids, 281 



(i) A Consideration of the Possible 



Origin of Species from Hybrids, . 282 



I. Introduction. 



With the advance of the present century an increasing amount of attention has 

 been given to the origin and relationship of plant hybrids. About 1719 Fairchild 

 raised a hybrid pink from two well-known parents, but hybrids seem first to have been 

 definitely recognised in the wild state, and artificially produced afterwards by Linnaeus, 

 whose work induced Kolreuter to carry out those laborious and careful investigations 

 and experiments which proved of the utmost value to his successors in the same field of 

 inquiry. Gartner still further confirmed and extended his results, while Herbert, 

 Wichura, Naudin, Naegeli, Darwin, Focke, and others have carried through detailed 

 observations on groups, which are of great scientific import. 



Many gardeners and nurserymen also early realised that new forms, often of great 

 beauty or striking habit, might be obtained by hybridisation, and thus a stimulus 

 was given to the artificial production of hybrids. 



In 1881 Focke published his Pfanzen-mischlinge, in which I reckon that at least 

 two thousand good hybrids are recorded. Many of these are of natural production, 

 and their parentage may be to some degree doubtful, but a large proportion has been 

 artificially produced, and the parentage is accordingly better vouched for in most cases. 



Hitherto, it may be said, observers have confined themselves almost entirely to noting 



VOL. XXXVII. PART I. (NO. 14). 2 H 



