1915] DE VRIES—OENOTHERA BIENNIS 171 
The endemics are rare, often strictly local, and grow in the midst 
of a luxuriant vegetation of their widely spread and _ thriving 
ancestors. It is hardly necessary to point out that this conclusion 
holds good not only for Ceylon, but for the origin of endemic and 
local species in general. 
Wu tls has also called attention to the Podostemaceae and 
the allied group Tristichaceae. They show one of the most inter- 
esting illustrations of a very rich differentiation without the least 
indication of a relation to their environment. A very great uni- 
formity in the conditions of life is combined with a most remarkable 
variety in their morphological structure. In the Podostemaceae 
the flowers are anemophilous, terminal, and erect, but combine 
with these characters of low organization the highest degrees of 
dorsiventrality and of differentiation, and this without any refer- 
ence to advantages or disadvantages to be derived from them in 
their functions. Numerous points of similar significance in the 
structure of the vegetative and reproductive organs are pointed 
out by the author. Moreover, the genera Tristicha and Podo- 
stemon, which are widely distributed, are comparatively little 
modified from the earlier types of the orders, while the highly 
specialized forms are at the same time the rarest, exactly as in 
the case of the endemics of Ceylon. 
In the group of the evening primroses the same principles 
prevail. Their struggle for existence is limited by the difficulties, 
which they have in producing roots. Cuttings almost never suc- 
ceed in rooting, with the exception of the lateral rosettes at the 
base of the stem. Artificial transplanting becomes difficult as 
soon as the main root increases in size. In the field only a small 
percentage of the seeds germinate and thrive, and this only under 
special conditions. ‘They want a stirred up soil and do not like 
to grow between other plants. These characters are common to 
all the forms which I have had an opportunity of studying in their 
native habitats. On the other hand, the numerous small specific 
i erentiations, such as the form of the leaves, the branching of 
the stem, or the structure of the flowers and fruits, do not show 
’ Wituis, J. C., On the lack of adaptation in the Tristichaceae and Podostemaceae. 
Proc. Roy. Soc. 8:532-550. 1914. 
