272 DR J. M. MACFARLANE ON THE 



In summarizing as to protoplasm and its modifications as plastids, where con- 

 siderable differences can be traced in the plastids of two parents the hybrid gives 

 excellent results. Only in a few parent plants have these differences been sufficiently 

 marked to allow of comparison with the hybrid. The leucoplasts in the epidermal 

 cells of the parents of Dianthus Lindsayi are very different in size, while most of 

 the leucoplasts in the hybrid are exactly intermediate, but from careful measurement of 

 lantern projection images of these it has been found that some very nearly resemble those 

 of the female parent. The chromoplasts of the petal cells in Geum intermedium and of 

 the sepal cells in Masdevallia Chelsoni are additional illustrations. Those of the former 

 are very variable in size and number, but this is probably to be explained from its 

 inheriting half of its hereditary features from Geum rivale, which is equally variable as a 

 species. Leaves of corresponding age and position from Saxifraga Andrewsii and its 

 parents have furnished chloroplasts of small size and dark green colour in one parent, of 

 large size and soft emerald green colour in the other, and an intermediate type in the 

 hybrid, though some diverge towards the " Geum " parent in having large chloroplasts. 



But the average size, shape, and lamellar deposition in starches of Hedychium 

 hybrids are perhaps the most interesting cases adduced. When we remember that these 

 are bodies formed temporarily as reserve food, and that they are built up by addition of 

 successive micellae through the agency of minute protoplasmic masses or leucoplasts, we 

 have a direct proof that these leucoplasts are themselves fundamentally modified. Their 

 activity in the cells of the hybrid is evinced by the building up of starch grains which, 

 though only of temporary duration in the history of the plant, are so accurately constructed 

 as to be an exact combination in appearance of a half corpuscle of each parent. 



Finally, we may recall the facts advanced as to colour, flowering period, chemical 

 combinations, and growth vigour, which, though scanty and fragmentary in their nature, 

 all point to the conclusion that hybrids are intermediate between their parents in general 

 life phenomena. 



VI. The Bearing of Hybridity on Biological Problems. 



A wide and attractive field for the biologist is still open in the investigation of plant 

 and animal hybrids. Though much work of a laborious kind has been expended on 

 the plant side, we must regard it merely as the small beginning to an inquiry that will 

 yield results of great value. On the animal side it may truly be said that all the results 

 are in the future. Such being the case, we can scarcely hope to do more at this stage of 

 the inquiry than indicate shortly what seem to be lights cast on certain hitherto 

 doubtful or intricate problems, from a minute study of plant hybrids. 



(a) Relative Potency of the Male and Female Sex Elements in the Formation of an 

 Organism. — This problem has greatly occupied the minds of biologists during the last 

 decade, and a solution has only been attempted hitherto from consideration of the 



