MINUTE STRUCTURE OF PLANT HYBRIDS. 273 



behaviour of the sex elements at, and immediately subsequent to, the period of 

 fertilisation. The tissues of hybrids shed a very exact light on the subject. No matter 

 what tissue or set of tissues are chosen, if the cells composing such are tolerably diverse 

 in the parents, one can trace with ease the modifying action which both sex elements 

 have had on them, while these clearly prove to us that each sex element, after union 

 with its complementary sex element, represents potentially half its former individuality, 

 or retains half its former hereditary properties. If one select, for example, a few 

 adjoining cells from the leaf epidermis of Dianthus Grievei and its parents, as figured in 

 Plate IV. figs. 1-3, and compare these, one sees that the average cell of the hybrid is an 

 exact mean between the cells of the parents. On comparing further the epidermal tissue 

 of a dozen hybrids, if one were to be guided alone by the number of epidermal cells and 

 of stomata over a given area, a like conclusion would be reached. In such special cases 

 as the sepaline gland of Philageria and Lapageria, we deal with cells resulting from 

 repeated division of a set of mother cells. To effect upbuilding of the hybrid 

 gland, therefore, proliferation of a set of cells takes place, each of which has a Philesia 

 heredity towards arrest of growth and a Lapageria heredity towards luxuriant cell 

 proliferation, the resultant being a gland built up of half as many cells as that of the 

 one parent. 



But Van Beneden * went further than most of his zoological co-workers were prepared 

 to go when he asserted that each cell in an organism is a hermaphrodite structure. To 

 this thesis many subsequently took exception, and with some show of reason perhaps, 

 seeing that no direct proof in individual cell life was forthcoming. But one is forced to 

 accept its absolute correctness from study even of one hybrid. It is this hermaphroditism 

 of the entire hybrid organism which not only impresses on it the structure that the 

 naked eye and microscope reveal, but which causes it to have a life cycle whose successive 

 steps are intermediate between the parent extremes. Thus sufficient facts are in our 

 possession, and will, we hope, be greatly supplemented ere long, to prove that the period 

 of bud-bursting, of leaf-expansion, of flower production, fruit ripening, and other vital 

 phenomena in hybrids are all dependent to a wonderfuHy exact degree on hereditary 

 inheritance. Naturally, when we make this statement, we wish it to be clearly understood 

 that secondary causes may modify or obscure the exactness of phenomena. Thus every 

 one who is practically conversant with plant life knows the powerful influence which soil, 

 moisture, situation, &c, have in altering the even tenor of a plant's way. It is on this 

 account that we would earnestly desire to have continuous and exhaustive experiments 

 carried out, where every possible care might be taken to eliminate disturbing factors. 



(b) Unisexual Heredity. — By this term we would designate the outcome of those 

 observations now recorded which prove that structures found only in one parent, and with 

 no corresponding counterpart in the other, are handed down, though reduced by half. 

 The sepaline honey-gland of Philageria, the small circumstomatic cellular knobs of 

 Saxifraga Andreivsii, the colour patches on the sepal of Cypripedium Leeanum, and the 



* Recherches sar la maturation de I'osuf, 1883. 



