30 THE PRINCIPLES OF HEREDITY 



proliferate into a complete individual. The power persists 

 longer in plants than in animals ; from a fragment of a 

 begonia leaf may arise an entire individual capable of con- 

 tinuing the race, the cells being turned from their original 

 destiny by a change in the environment. But among the 

 higher plants this power of reproducing the entire individual 

 by means of cells other than germ-cells, or what may 

 normally proliferate into germ-cells, is, as a rule, less com- 

 plete. 1 Often all that appears to persist is the power of 

 reproducing from such fragments of the complete organism 

 as contain cells which might normally proliferate into germ- 

 cells, the parts wanting to render the fragments complete 

 organisms. Thus a geranium slip, for instance, contains cells 

 which normally (i. e. when the branch remains a part of the 

 plant) proliferate into germ-cells. If this branch be bedded 

 out as a slip, it produces the roots which are needed to con- 

 vert it into a complete organism of its species. Here germ- 

 cells are not produced from cells not destined to that purpose 

 as in the begonia leaf, but lost parts are reproduced by what 

 may be termed, and in fact is, an exaggerated process of 

 healing. In other plants the power of reproducing lost parts 

 seems to be on an even smaller scale, and only comparatively 

 trifling injuries are healed i. e. a small fragment does not 

 reproduce the whole, though the whole may reproduce small 

 fragments. 



52. Among animals, owing to the greater specialization of 

 the cells, and the more complex conditions under which they 

 live, this power of reproducing lost parts is present, in 

 general, to a much less extent than among plants. At least it 

 is present to a much less extent in the adult. In the embryo, 



1 This statement has been disputed. " We have no means of estimating 

 exactly the proportional number of cases in which this is possible, either 

 among the lower or the higher plants, but it is certainly much greater 

 than Weismann supposes. * How is it that all plants cannot be repro- 

 duced in this way ? 3 he asks and then adds : ' No one has ever grown a 

 tree from the leaf of a lime or an oak, or a flowering plant from the leaf 

 of the tulip or the convolvulus.' But I am told by botanists that the 

 only reason why the phenomenon thus appears to be a rare one, is 

 because it is not worth any one's while to grow plants in this way at a 

 necessarily unsuitable season of the year. Thus, the Rev. George 

 Henslow writes me : * The fact is that any plant will reproduce itself by 

 its leaves, provided the cells be " embryonic " (i. e. the leaf not too near 

 its complete development), and that it be not too thin, so as to provide 

 nutriment for the bud to form till it has roots.'" (Weismannism, by 

 Professor G. Romanes, pp. 52-3.) However, even if Mr. Henslow's 

 statement be correct, the statement in the text is not affected, since the 

 fragments of some species of plants give origin to new individuals much 

 more readily than the fragments of other species. 



