360 PROVISIONAL HYPOTHESIS Chap. XXVIL 



Graft-Jiyhrids. — It is well known from innumerable trials 

 made in all parts of the world, that buds may be inserted 

 into a stock, and that the plants thus raised are not affected 

 in a greater degree than can be accounted for by changed 

 nutrition. Nor do the seedlings raised from such inserted 

 buds partake of the character of the stock, though they are 

 more liable to vary than are seedlings from the same variety 

 growing on its own roots. A bud, also, may sport into a new 

 and strongly-marked variety without any other bud on the 

 same plant being in the least degree affected. We may there- 

 fore infer, in accordance with the common view, that each 

 bud is a distinct individual, and that its formative elements 

 do not spread beyond the parts subsequently developed 

 from it. Nevertheless, we have seen in the abstract on 

 graft hybridisation in the eleventh chapter that buds certainly 

 include formative matter, which can occasionally combine 

 with that included in the tissues of a distinct variety or 

 species ; a plant intermediate between the two parent-forms 

 being thus produced. In the case of the potato we have seen 

 that the tubers produced from a bud of one kind inserted into 

 another are intermediate in colour, size, shape and state of 

 surface ; that the stems, foliage, and even certain constitutional 

 peculiarities, such as precocity, are likewise intermediate. 

 With these well-established cases, the evidence that graft- 

 hybrids have also been produced with the laburnum, orange, 

 vine, rose, &c., seems sufficient. But we do not know 

 under what conditions this rare form of reproduction is 

 possible. From these several cases we learn the important 

 fact that formative elements capable of blending with those 

 of a distinct individual (and this is the chief character- 

 istic of sexual generation), are not confined to the repro- 

 ductive organs, but are present in the buds and cellular tissue 

 of plants ; and this is a fact of the highest physiological 

 importance. 



Direct Action of the Male Element on the Female. — In 

 the eleventh chapter, abundant proofs were given that 

 foreign pollen occasionally affects in a direct manner the 

 mother-plant. Thus, when Gallesio fertilised an orange- 

 flower with pollen from the lemon, the fruit bore stripes 



