CANNON: StupIES IN PLrant Hysrips 151 
-even in the details, and his conclusion that the parents share 
equally in transmitting their respective characters. 
Farmer * studied the structure of Polypodium Schneideri, which 
is a hybrid between P. aurenm and P. vulgare. The hybrid was 
reproduced by Farmer. The study showed the hybrid was not 
strictly intermediate either in form or structure. 
In the following section of this paper I shall consider the rela- 
tion of the results of the cytological studies of hybrids as above 
- outlined, as well as of my own to be given later, to the variation 
of the hybrid race, but I may refer in this place to one or two 
considerations in connection with the possible bearing of the struc- 
tural studies on the same topic. It is to be noted that Macfarlane 
studied only intermediate forms, but on the other hand the fern 
hybrid of Farmer’s investigations was intermediate neither in form 
nor in structure. These apparently contradictory results raise the 
very interesting question, are hybrids, whether intermediate in form 
or not, always so in structure? Or can it be that variation in 
form is also associated with differences in structure? A careful 
histological study of hybrids that are clearly not intermediate, as 
for instance those following Mendel’s Piswm-type could not fail to 
give most interesting results. And it may be added that the 
results from such study might be of importance in determining the 
hybrid status of the form. 
THE RELATION OF THE CYTOLOGICAL TO THE EXPERIMENTAL 
Strupigs OF HYBRIDS 
The task of the cytologist in the study of plant hybrids is 
primarily that of observing the relation of the manner of forma- 
tion of the sex-cells to the variation of the hybrid itself, and it 
should for that reason include the study of hybrids which have 
yielded definite results from experiment, such forms, for example, 
as the Pisum-type. Owing however to the recentness of the dis- 
covery of the Mendelian laws, studies of this character have not 
been carried on, as far as I know, and conclusions to cover special 
Cases of variation, for instance the Psu-type, must therefore be 
regarded as tentative merely. Beyond this, general considera- 
tions, such as the fertility or infertility of the hybrid and the form 
oS tae ee ne 
*% Farmer, On ‘es Sheers of a Hybrid Fern. Ann. Bot. 11: 533- 1897. 
