566 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING. 



been made in recent times into the minute structure of plant-hybrids is by Mac- 

 farlane. He selected a number of hybrids, and worked through their anatomy 

 from base to apex in the most painstaking manner. He dealt with roots, stems, 

 leaves, and the various portions of the flower, always comparing their various 

 tissues (both as regards size, form, and distribution) with those of their parent- 

 forms. And his result is to confirm what has been written above, though it is 

 obvious he had never read these pages. Amongst the more interesting of his 

 results may be mentioned those on starch-grains. Of course in a great many of 

 the parent-forms uniting to form a hybrid there is no recognizable difierence in the 

 size or structure of the starch-grains. But in the genus Hedychium (belonging 

 to the family Zingiberaceae) exceptions to this rule were found. Thus, those of 

 Hedychium Sadlerianum are intermediate in form and size between those of its 

 two parents, H. Gardnerianum and H. coronarium; and those of a hybrid between 

 H. elatwm and H. coronarium exhibited similar intermediate characters. 



It is important to note also that the aromatic substances and colouring matters 

 produced in the cells of a hybrid are inherited partly from the maternal, and partly 

 from the paternal stock. As we have several times already had occasion to mention, 

 the various species of the Rose genus may be recognized at once by their peculiar 

 scent. The perfume of Rosa Centifolia is the one which in particular is understood 

 by the rose-scent, but it is very different from that of Rosa al^ina, and the latter in 

 its turn is unlike any of the scents emitted by Rosa arvensis, R. Gallica, R. Indica, 

 &c. Rosa Nasterana has a scent strongly resembling that of Pinks, whilst Rosa 

 lutea and R. punica are notorious for their disagreeable smell. Now the hybrid 

 Roses emit odours in which the scents of the parent-species are merged together in 

 a great variety of ways. Usually the scent of one stock predominates, and there is 

 only a suggestion of the other. Sometimes, however, an entirely new scent is 

 evolved from the fusion of the two, as is the case, for instance (according to Mac- 

 farlane), in Hedychium Sadlerianum, the hybrid between H. Gardnerianum and \\ 

 H. coronarium; and, again, in other cases, one of the component odours is inten- 

 sified and the other is extinguished. The same statement applies to the aromatic 

 substances to which the scent of the foliage is due. The hybrids of Rosa 

 glutinosa, Rosa rubiginosa, and R. rugosa, with Rosa Gallica and R. Centifolia, 

 are very interesting in this connection. The aromatic substances which are con- 

 tained in fruits and excite our nerves of taste are also inherited, partly from the 

 maternal and partly from the paternal stock. Owing, however, to the difficulty of 

 naming the various sensations of smell and taste it is of little use to discuss the 

 subject more fully. 



As regards the colouring-matters reproduced in hybrids the first point to notice 

 is that in cases where the foliage is of different shades of green in the parent-species 

 the leaves of the hybrid exhibit a shade intermediate between the two. Conspicuous 

 instances of this are afforded by the hybrid Willows derived from Salix nigricans 

 and S. purpurea. In both these species the foliage becomes black when it withers, 

 and this characteristic is transmitted, though not in its full strength, to the hybrids 



