OCCURRENCE AND INHERITANCE OF SEX INTERGRADATION IN PLANTS 27 
flowers are male and their later flowers in part male and in part female, 
(4) individuals whose first flowers are male and their later flowers female, (5) 
individuals exclusively male. 
Schulz (1892), on the basis of eleven years' observation of the ash (Fraxi- 
nus), recognizes ten distinct forms: 
(1) Individuals which bear only male flowers. 
(2) Individuals which bear only hermaphroditic flowers. 
(3) Individuals which bear only female flowers. 
(4) Individuals which bear only male flowers one year and the next 
year show branches of both male and female flowers. 
(5) Males which have certain branches either female, hermaphroditic, or 
with both kinds of inflorescences. 
(6) Individuals which one year bear only female flowers, and the next 
year have branches with more or less hermaphroditic and female flowers. 
(7) Individuals bearing equal numbers of female and hermaphroditic 
flowers on the same or different branches. 
(8) Individuals which bear one year only hermaphroditic flowers and 
almost always associated with them female flowers, later producing male 
flowers. 
(9) Female or hermaphroditic individuals with male branches. 
(10) Individuals with about equal numbers of male, hermaphroditic, 
and female flowers. 
Correns (1908) says that- there are at least thirty intergrading cate- 
gories recognizable in Plantago lanceolata. In his classification of forms for 
experimental purposes he recognizes the following classes: (i) hermaphro- 
dites, (2) predominantly hermaphrodites, (3) hermaphrodites and females, 
(4) predominantly females, and (5) females. 
I have given only a few examples of the very many that are listed in 
the plant kingdom, but the forms cited are sufficient to show the wide range 
of intersexuality that exists among plants. These cases of intergrades in 
functional and structural development of the sex organs, taken in connection 
with the classes based on the distribution of the sex organs by plants as 
individuals as tabulated above, present an almost bewildering complete- 
ness as a picture of the theoretically possible gradations in sex characters 
both of the gametes and of the organisms which produce them. And it is 
to be remembered that for the most part these are not exceptional or chance 
cases. They represent the common and obvious facts as to sex in the 
flowering plants. No theory of sex based on the assumption of the alter- 
native inheritance of fixed sex factors which are segregated at the time of 
the reduction divisions can do justice to the conditions presented in the 
higher plants. 
I have brought together data as to the distribution of sex forms in the 
various orders of seed plants. For this purpose I have followed Engler and 
Gilg's "Syllabus der Pflanzenfamilien." Practically every order has fami- 
