382 REV. GEORGE HENSLOW ON THE 
the female organs are seldom affected, or merely become precocious in their development. The cause S 
of this affection is doubtful, and is different in different cases. ...... The contabescent plants of | 
Dianthus and Verbascum found wild by Wiegmann grew on a dry and sterile bank." 
Though there may be more than one cause, I should feel strongly inclined to think 
that in the majority of instances it is correlated with a lessened degree of dichogamy, ~ 
if not always with self-fertilization, which Mr. Darwin himself gives as an “ additional | 
cause." The last sentence above points, however, to the chief probable cause being - 
nutrition. 
10. The relative fertility may equal or surpass that of crossed plants. 
The fertility of self-fertilized plants, observes Mr. Darwin (7. c. p. 326), * ranges from ` 
zero to a fertility equalling [or exceeding] that of the crossed flowers ; and of this fact 
no explanation can be offered." As examples of plants of which crossed and self-fertilized — 
flowers produced a nearly equal number of seeds are Ipomea purpurea, Gesnera pen- ` 
dulina, Salvia coccinea, Limnanthes Douglasii, Lobelia fulgens, and Nolana prostrata; — 
yet “ thé plants raised from the crossed seeds exceeded considerably in height those | 
raised from the self-fertilized seeds." He rightly considers that ** the average number of | 
seeds per capsule is a more valuable criterion of fertility than the number of capsules | 
produced.” By selecting all cases from his Table D, of ** Relative Fertility of Plants of 
Crossed and Self-fertilised Parentage,” which give the ratio of the number of seeds per ` 
capsule, I find it to be about 100 : 92 for the crossed to the self-fertilized, a result not far | 
from equality. The two examples where the self-fertilized surpassed the intercrossed ` 
were the cleistogamous flowers of Vandellia munmularifolia (100 : 106) and the third | ; 
generation of Dianthus Caryophyllus (100 : 125). It has already been shown how the ` 
ratio of the fertility of the self-fertilized plants of Ipomea purpurea and Mimulus luteus ` 
gradually equalled and then surpassed that of the intercrossed plants. | 
ll. The fertility or the health of either cultivated and artificially or wild and naturally 
self-fertilized plants does not necessarily decrease in successive generations. 
Mr. Darwin says, * There is no evidence at present that the fertility of plants goes — 
on diminishing in successive self-fertilised generations." He is here alluding to the ` 
results of his cultivated plants; but it is evidently equally true of all common self- - | 
fertilizing weeds. Chickweed, Groundsel, Shepherd's-purse, and Poa annua have probably — 
flourished for centuries just as they do now, and are as vigorous at the present day and : 
doubtless as fertile as ever they were. A rapid succession of ripening capsules may ` 
compensate for any want (if any) of a copious supply of seeds in individual capsules. 
Again, besides having the power to propagate adequately, the self-fertilized may be as 
healthy as the intercrossed after any number of generations. In support of this latter 
statement is the fact that the intererossed plants did not exceed the self-fertilized in — 
height in greater and greater degrees in successive generations; but the reverse was 
the case; for the mean ratio of the first three generations of the intercrossed to the | 
self-fertilized plants of Zpomea was 100:74°3; that of the second three as 3 100: IT 6 
| that of the third three as 100 : 81-6. The ratios thus gradi ally a ate 5 
80 that instead of the xatio noone a smaller fraction, etm u 
