2 OBSEKVATIONS UPON MULING AMONG PLANTS. 



will most probably repay repeated experiments. It has been 

 lately ascertained that moistening the stigma with the honey 

 secreted by the flowers promotes the fecundation of the ovarium 

 of these plants, and, doubtless, since no impregnation can be 

 effected before the separation of the lobes of the stigma, because 

 the pollen adheres to it in consequence of such treatment until 

 the division takes place. 



Though, however, the influence of the sex of the parent is not 

 in general exhibited, as in animals, by any outward signs, yet 

 there is often a great difference in the inward constitution of the 

 plants produced by cross impregnation. It is, for instance, by 

 no means a matter of indifference whether Nicotiana rustica be 

 impregnated with the pollen of N. paniculata, or the contrary. 

 In the former case the mule is more fruitful than in the latter, 

 and other similar instances might be adduced. 



In intermediate impregnation, however, it appears to be of no 

 consequence whether tlie male or female be the intermediate 

 species. Nicotiana chinensis, for instance, produces the same 

 mule with N. rusiico-paniculata that it does with N. paniculato- 

 rustica. 



Tlie author very justly considers this identity of type in the 

 mules arising from covuiter-impregnation as a very strong argu- 

 ment against Schleiden's notion of the production of the embryo 

 from the extremity of the pollen tube. Two different kinds of 

 pollen could scarcely be expected, if such were really the case, 

 to produce two perfectly identical plants. And the same in- 

 ference may be drawn from the fact that in the production of 

 double blossoms, it is a matter of indifference whether the pollen 

 be taken from a double or single variety, provided the flower of 

 the matrix is double. 



It is not necessary to go through the facts adduced in the 

 chapter relative to the normal types produced by impregnation 

 between two pure species, as those of most importance have been 

 already mentioned incidentally. Sliglit changes occur from time 

 to time ; but this is nothing more than takes place in raising 

 seedlings from the pure species themselves without any cross 

 whatever. The grand point in all experiments is to secure the 

 parent plants in as pure a state as possible ; and where practi- 

 cable, to select species from the woods and fields, and even these 

 as near the normal form as may be. Where proper pains are 

 taken, exceptional forms are very rare, perhaps one only from 

 the produce of many capsules. Some genera and species seem 

 to have a greater disposition to produce such forms than others, 

 as for instance Dianthus, Digitalis^ Lobelia., Passijlora, NicO' 

 tiana, and Verbascum, and sometimes this tendency is confined 

 to a single species of a genus. When, however, numbers of such 



