$02 
R. H. Compton. 
same species : it was thus necessary to assume that in respect of 
the mechanism of fertilisation every individual plant differed 
markedly—chemically or structurally—from every other. This 
assumption is almost unthinkable and numerous attempts have 
been made to show that it is in fact incorrect. Indications were 
not wanting that cross-pollination does not always give uniformly 
good results. For instance Muller (1873) found that in self-sterile 
species of Abutilon there is often more or less complete failure to 
set seed in crosses between closely related plants, e.g., between 
parents and children, between sisters, and between half-sisters. 
Morgan (1905) too, as a result of extensive experiments on Ciona. 
intestinalis, came to the conclusion that “ it is not true that the 
sperm of a given individual will fertilise equally well the eggs of al 
other individuals.” 
VI. —The Work of Correns. 
Correns (1912) has recently made a partially successful attempt 
at solving the problem of the sterility of near kin inter se. He 
assumes that self-sterility is due to the presence of inhibitory 
substances ( Hemmungsstoffe ), but does not thereby wish to prejudge 
the question whether they are true inhibitors or whether they 
represent the lack of the means of furthering pollen germination 
and growth. The problem can therefore be stated as follows: 
Are these inhibitory substances individual ( Individualstojfe ) or are 
they racial and hereditary ( Linienstojfe ) ? Correns reduced the 
experiment to its simplest form by taking two individuals (called 
B and G) of Cardamine pvatensis of distinct origin, and crossing them 
reciprocally. The offspring (which may for our present purpose 
be considered together) were tested individually by pollinations 
(1) from the parents, (2) on the parents, and (3) from sisters. The 
results were far from simple, as the degree of fertility fluctuated 
widely, but Correns was able to draw from them the highly 
interesting conclusion that self-sterility depends on racial hereditary 
factors and is not a purely individual phenomenon. 
The experiments in which the F x plants were pollinated from 
their parents B and G are the most instructive. It was found that 
these fell into four distinct classes according to their behaviour, as 
follows:—(1) Plants fertile with both B and G : these are regarded 
as lacking both the inhibitors which rendered B and G self-sterile, 
and may be written bg. (2) Plants sterile with both B and G, and 
therefore considered to have both of the inhibitors: these may be 
represented as BG. (3) Plants fertile with B, sterile with G (written 
