Recent Advances in the Study of Heredity. 275 
characters of Pisum supplies us with suitable, and easily obtainable, 
material. 1 
Unlike the characters which we have considered hitherto, and 
belong to a very early stage in the life-history of the plant, the 
characters to which I now refer are not manifested until the plant 
is ripe and dry. They belong to the seed-coat of the ripe seed. One 
of them is a rather beautiful brown mottling on a paler and 
brownish background ; to be more precise, it consists of a network 
of anastomosing brown areas between the interstices of which the 
paler brownish background is seen. Peas with this type of coloration 
are called Maple or Partridge Peas ; and a pennyworth from a 
corn-chandler furnishes ample material for starting an experiment 
with. Carter’s “ Grey Pea ” belongs to this type ; so also does the 
Pisum arvense punctatum offered by Messrs. Haage & Schmidt, of 
Erfurt. 
Another of the types of coloration which the seed-coat of 
Pisum may exhibit, consists of a greyish background over which is 
distributed pretty evenly a very large number of minute dots of an 
intense purple. The size of the dots is not uniform, but the limits 
of its variation are not very widely separated : the dots sometimes 
tend to “ run,” as if the paper had been wet when they were put 
on. The “ French Sugar Pea ” offered by Messrs. Sutton, and the 
Pisum Jomardii of Messrs. Haage & Schmidt’s catalogue afford 
good instances of this type of coloration. I mention these 
instances so that the reader may, if he wishes, carry out the 
experiment I am about to describe. It is perhaps hardly necessary 
to say that if he is engaged in teaching it is very desirable that 
this should be done. The labour and expense are trifling ; and the 
results are almost indispensable to an adequate demonstration of 
the subject. 
For the sake of brevity we will call the Maple character M ; 
and the purple spot character P. The result of crossing a Pea 
bearing the M character with one bearing the P character is a Pea 
whose seed-coats bear both these characters. At first this sounds 
very much as if the result of this mating were a blend ; and it is 
not impossible that a careless searcher after instances of exceptions 
1 It is interesting to note how closely the theory enunciated in 
this paragraph resembles De Vries’ conception of the nature 
of the Mendelian pair of characters. To De Vries, likewise, 
only one character is concerned in a Mendelian pair : but, 
according to him, the two units are not occasioned by 
presence and absence of a single unit, but by patency and 
latency of such a unit. See Mutationstheorie, II., p. 643, etc. 
