1916} HOAR—STERILITY IN RUBUS 379 
and Malus are notorious for the forms resulting from interbreeding. 
By analogy we should expect the same condition of things in 
Crataegus.” 
Rubus presents a condition of things quite like that of Crataegus. 
Although Gray’s Manual of the last edition contains 38 species 
all told, yet the authors carefully state that in Eubatus we have 
“a group of great taxonomic difficulty, in which many species 
have been recently proposed. Of these the better marked have 
been here freely included, but without entire confidence that the 
future intensive study may not show them to be intergradient and 
perhaps in many cases hybrid forms.’”’ Because of this great varia- 
tion and because of the uncertainty as to which are and which are 
not true species, I have selected this genus in which to make a 
careful study of the pollen conditions. However, before proceeding 
to the results of my research, it seems best to give a brief historical 
account of Rubus and the work done upon it up to the present time. 
Rubus, like Crataegus, has had an almost miraculous growth in ~ 
number of species within a few years. Only 18 years ago GRAY’s 
Manual recognized but 3 species and 2 varieties for New England, 
and, as BRAINERD (33) remarks, 2 of these specific names were 
wrongly applied. In 1898 BatLey (34) published his Evolution of 
native fruits in which he recognized 13 species of Rubus of the 
Eubatus group for New England. Since that time BLANCHARD 
has published detailed descriptions of 40 or more forms, most of 
which he has considered as species. Many of these, as I shall show 
later, appear to be of hybrid origin from a study of the pollen; but 
from an external study alone he came to the conclusion that they 
were worthy of specific rank. 
In 1911 BIcKNELL (35), in an article entitled “Have we enough 
New England blackberries?” makes the following statement: 
“The least unstable species (here) possess some kind of ready pliancy 
which answers often with marked emphasis to slightly changed con- 
ditions of growth, and further, all the species by some freely practised 
method of versatility acquire variously in combination with their own 
proper characters the features of associated members of the group.’ 
He adds that these facts impart an extraordinary natural variability 
* The writer is responsible for the italicizing. 
