590 
Cross-fertilisation of Cereals. 
flower, and so commend themselves to the purchasers of plants, 
are the more valuable because they are unique plants, incapable 
of reproducing themselves. But it is very different with the 
agriculturist, whose object is to get the largest quantity of seed 
of the best quality. Hybrid plants must be avoided even 
though it can be shown that the seeds of the second generation 
are capable of generation. 
The fertilisation of pollen from a widely separated species of 
the same genus (6) is difficult, and the seeds of the hybrid are 
very rarely fertile. Still more difficult and rare is fertilisation 
when the pollen is obtained from a plant belonging to another 
genus (7). Yet fertile seeds have in several cases been thus 
produced in plants cultivated for their flowers ; and an instance 
is recorded of fertile seeds being produced by a hybrid between 
plants belonging to different genera of cereals. Mr. A. Stephen 
Wilson made over four hundred experiments to fertilise plants 
of wheat, rye, barley, and oats with pollen from each other ; but 
he failed except in two cases in which he applied the pollen of 
rye to the pistil of wheat. The two seeds produced in this way 
germinated, and developed into plants which were intermediate 
between the two parents, but the pollen never ripened, and the 
ovules not being fertilised no seed was produced. 
From what has been said it is obvious that attempts to pro- 
duce improved varieties of cereal crops must be limited to the in- 
dividuals of a single species, including under the term species 
all the cultivated as well as natural varieties. But no original 
wild form is known of any of our cultivated cereals, though they 
belong to genera which have wild species. Even in our British 
flora there are three indigenous species of the genus to which 
wheat belongs, viz. Triticum caninum (Huds.), T. r opens (L.), and 
T. junceum (L.) ; four species of the genus to which barley belongs, 
Hordeum sylvaticum (Huds.), II. pratense (Huds.), II. murinum 
(L.), and II. maritimum (With.) ; and three species of the genus 
to which the oat belongs, Arena fatua (L.), A. pratensis (L.), 
and A. pubescens (L.). 
Having been from the earliest times under culture, the 
cultivated species are represented by a large number of fixed 
varieties, and of these it is very difficult to discover which 
most nearly represents the primitive form. Indeed it is often 
hard to determine whether the cultivated forms of each of the 
genera belong to one or more original species. Seven distinct 
types of cultivated wheat are easily distinguished. These are 
the following : 
1. Triticum monococcum (L.), which has a single grain in each 
spikelefc, and the pale divides into two when ripe. 
