OBSERVATIONS UPON MULING AMONG PLANTS. 3 



exceptional plants spring from the same seed, as from Verbascum 

 phceniceo-aKsfriacum, Dlantlius arenario-'pulcliellus^ «S:c., or 

 when, on repeated experiments with the same species, the excep- 

 tional type occurs either singly or in numbers, the individuals 

 have as complete a resemblance amongst each other as the norma,l 

 mules; no variations or transitional forms occur, as is the case 

 where the parents are hybrids : they are for the most part decided 

 types. It is observed too, that neither the male nor female 

 element has an exclusive influence in the formation of such ex- 

 ceptional types, thougli they exhibit usually a decided predomi- 

 nance either of the character of the male or female parent, the 

 unusual potency of the one or the other having given rise to the 

 abnormal form. Most of them are absolutely sterile, a point 

 which makes the study of them extremely difficult and vexatious ; 

 and even where they are fertile, as in Dianthus arenario-puU 

 chellus, there is a tendency, like that so well known amongst 

 animals, and to which the term Atavism has been given, to 

 revert to the ancestral type. 



Occasionally, however, especially in plants which have been 

 long cultivated, or amongst species which at the same time have 

 a very intimate elective affinity, and are so closely allied to each 

 other that they seem merely marked varieties, such as Matthiola 

 annua and glabra^ Malva sylvestris and Mauritiana^ Lychnis 

 diurna and vespertina, Primula elatior and officinalis, differences 

 of form and colour occur amongst the typical hybrids which 

 have no constancy, and which cannot be obtained with certainty 

 on repeated experiments. These differences are generally such 

 as are manifest only in the living plant, as in the degree of 

 roughness, undulation, viscidity, &c. It is supposed by Mr. 

 Herbert, that variations of this kind arise from the application of 

 a quantity of pollen insufficient to produce a real typical mule, 

 though potent enough to effect slight changes. To this notion, 

 however, the author is opposed, on the ground that experiment 

 seems to show that the completeness or incompleteness of im- 

 pregnation influences merely the perfection of the fruit and 

 seeds, and that a quantity of pollen insufficient for the impreg- 

 nation of an ovarium produces only imperfect fruit and seeds, 

 but gives rise to no distinct type ; for unless a proper quantity of 

 pollen be applied, the seeds are never perfected, or the embryo is 

 inert. Direct experiments also show that the time of impregna- 

 tion, whether early or late, be the state of the stigma what it 

 may, has no influence on the produce. 



No such deflections from the normal type of the mules have 

 occurred to the author in plants brought immediately from the 

 woods or fields, but only amongst individuals which have been 

 long under cultivation. 



It appears from experiment, that where impregnation takes 



B 2 



