178 
THE PLANT WORLD. 
Some go so far as to ask, For what purpose does a plant produce 
cleistogamous flowers, implying some kind of consciousness in the 
plant. 
But direct adaptation may be considered as resulting from the 
action of external forces, without involving in any way psychic 
factors, nor assuming that of all the possible reactions only useful 
ones will occur. 
To the question whether cleistogamous flowers are merely cases 
of arrested development or special adaptations of structures for 
securing self-pollination, various answers have been given. Asa 
Gray considered them as simply “ arrested buds.” But there 
are many “ arrested buds ” that are not cleistogamous, even in 
species that do regularly produce cleistogamous flowers. Cleis¬ 
togamous flowers are characterized by the fact that notwithstand¬ 
ing the arrested development, the pollen-grains and ovules reach 
maturity and they produce seed. This condition is somewhat 
analogous to that of dwarfing as a result of insufficient nutrition. 
In a dwarfed plant flowers and fruit occur earlier than normally, 
though not, of course, so abundantly. 
A further analysis of the characteristics of cleistogamy may be 
aided by noting Sachs’ division of the growing period of a plant 
into the morphological (in which the rudiments or the primordia 
of the organs are laid down in their propef numbers and posi¬ 
tions, and in which their early growth takes place) and the phys¬ 
iological (in which the organs enlarge to their proper size and 
attain their functional maturity). In cleistogamous flowers the 
morphological period is more or less shortened, but the physiolog¬ 
ical maturity does not seem to be affected, as far as the essential 
organs are-concerned. 
Darwin believed that while cleistogamy might in many cases 
be primarily the result of arrest in the development of the perfect 
flowers, it was in other plants a special adaptation for self-polli¬ 
nation or for the protection of the pollen. 
It remains therefore to be discovered, first, whether there are 
essential structural differences between chasmogamous and cleis¬ 
togamous flowers which are not due merely to differences in the 
degree of development, and second, what the causes of the abor- 
