318 REV. GEORGE HENSLOW ON THE 
but of different stocks, all the preceding being of exactly the same form of species; 
(5) crossing different varieties of the same species. 
Dean Herbert, in his work on the Amaryllidee (p. 371), published in the year 1836, 
makes the following remark :— 
* I am inclined to think that I have derived advantage from impregnating the flowers from which I 
wished. to obtain seed with pollen from another individual of the same variety, or, at least, from 
another flower rather than its own, and especially from an individual grown in a different soil or 
aspect.” 
As far as I am aware, such a surmise has been generally accepted by horticulturists 
and botanists to the present time, but more as a general assumption than as one based 
on strictly scientific experiments; and it is the great merit of Mr. Darwin that, just as 
he established, on scientific grounds, the value of intererossing by insect agency, 
so well illustrated by Sprengel in 1790, so, in his present work, he has done the same for 
Dean Herbert’s inferences. He has thus placed on a scientific basis the exact value of | 
such crossings. 
Of the results thus anticipated by Dean Herbert, Mr. Darwin has proved incontestably 
that the greatest benefits are derived by crossing individuals which have grown in dif- 
ferent localities, so as to acquire different constitutional peculiarities, though they may not 
be perceptible in their external appearance, or else, if differences be visible, they consist 
of some slight characters, which render one a subvariety of the other. When such plants 
are crossed, the offspring raised exhibit, as a rule, greater weight, more vigour in branch- 
ing, a darker foliage, more blossoms, an earlier period in flowering, &c., than those of 
their parents. 
Such beneficial results, however, are not absolutely invariable. Mr. Darwin LS 
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cases where but slight or even no benefit accrued to the plants raised from the seed 1 
of the crossed plants; but that, on the other hand, the self-fertilized plant beat its - 
crossed opponent in height &c., with which it was put in competition. Such, for ex- 
ample, was the case with a tall, highly self-fertile individual of Ipomea purpurea, to 
which Mr. Darwin gave the name of * Hero."  Eschscholtzia californica, Petunia vio- 
lacea, and Mimulus luteus are other instances. pe: 
The next degree of advantage of crossing was with individuals of the same stock, 
i.e. grown for many generations in the same soil and under similar conditions; and 
which therefore were probably all descended from the same parentage. With these the 
advantages of crossing were apparent at first, but after a few generations the com- 
parative results between such intercrossing and self-fertilization gradually approximated — 
uniformity. 
The third kind of union is between flowers on the same plant. And here Mr. Darwin | 
has corrected a hitherto widespread supposition, that it was beneficial for flowers to be 
thus crossed. It would seem, however, that such may do little or no good at all. Un- 
fortunately Mr. Darwin has not experimented to any great extent upon such a union ; 
and it would be unwise to generalize from so few instances. Collecting the various 
. items from his work under this head, they may be tabulated as follows, where 100 is | T 
placed as the standard for height or weight of the intercrossed :— 
