77S PART IV. — THE PHYSIOLOGY OF PLANTS. 



cold, time of flowering and fruiting, etc. : in fac^, when, for 

 instance, a number of seeds are produced by hybridisation, none of 

 the resulting seedlings may be intermediate in character between 

 the two parents, but some may quite resemble the one parent, and 

 the remainder the other. When the hybrids are intermediate in 

 character, the blending of the parental features may manifest 

 itself in different degrees ; it may be slight, as for instance when 

 a hybrid of parents with differently coloured flowers, bears flowers 

 of the two distinct colours : or more intimate, as when in such a 

 case the hybrid bears flowers with blotches or stripes of the two 

 colours ; or complete, as when in the same case the flowers of the 

 hybrid are of a tint intermediate between the colours of the 

 parental flowers. The same peculiarities are presented, of course, 

 by other structures ; for instance, as regards the colour, size, 

 flav^our of fruits, the size and shape of leaves, etc. 



One of the most remarkable aspects of heredity in plants is its 

 relation to the alternation of generations. When the life-history 

 of a plant presents a regular alternation of sporophyte and gameto- 

 phyte, it is the alternate, and not the successive, generations 

 hich resemble each other; sporophyte resembling sporophyte, 

 gametophyte resembling gametophyte. The hereditary character- 

 iistics of the sporophyte, for instance, are not presented by the 

 I gametophyte, which, though it springs from it, is commonly an 

 ; altogether dissimilar organism, but are transmitted through the 

 jgametophyte to the succeeding gamogenic sporophyte. This is 

 I not only obviously the case in plants, such as Ferns, in which the 

 /alternate generations are distinct organisms; but it is equally 

 • true of the plants, such as Bryophytes and Phanerogams, in which 

 I the alternate generations remain more or less intimately connected. 

 Variation is the term used to express the fact that an organism 

 may differ more or less widely from its parent or parents, present- 

 ing often some altogether new characters. 



It is in connexion with sexual reproduction that vaiiation is 

 most frequently manifested. It may, in fact, be generally stated 

 Ithat variation is more frequent and more marked, the more re- 

 /mote (within the limits of sexual aftinity) the relationship between 

 the two parents : thus variation is most common in the offspring 

 of individuals of different species ; frequent in the offspring of 

 two individuals of different varieties of the same species; least 

 common in the offspring of two individuals of the same species or 

 variety. 



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