Studies in the development of the sexual tissues in the genus rhododendron

Abstract

From a comprehensive survey of the facts brought forward in this study certain general conclusions may be stated for the majority of .members of the genus Rhododendron:

(a) A definite interval of time elapses between the flowering period of one year and the attainment of any stage in the development of the floral organs for the succeeding year, This interval varies according to the species and is longer in the case of the spring-flowering species than in the summer-flowering species, It extends over two growing periods.

But this definite interval of time may be ,altered, e.g., R. Keysii.

(b) At the onset of the winter period the stages reached in the male and female tissues of the majority of species is the same - the pollen-tetrad stage for the male tissues and placentae fully formed with ovular constrictions showing for the female tissues.

(c) But no winter dormant period may occur, e.g., R. Keysii, although the male tissues may still have a brief dormant period. The male tissues in the bud develop more rapidly than the female in all species.

(d) There is a correlation between the rates of development of the male and female tissues - certain definite stages in the one set of tissues corresponding to certain definite stages in the other set of tissues - and this for all species bearing normal flowered inflorescences.

(e) The flower-buds pass through a period of more or less complete dormancy during the winter period. Even when there is no winter period, e.g., R.Keysii or when the external conditions are suc-í that winter conditions are ameliorated as in the species grown under glass, a dormant period, of the male tissues at least, is still included in the cycle of development.

(f) There is a definite interval of time elapsing between the occurrence of the male and female reduction divisions:

But this interval of time may be altered, e.g., R. Keysii.

(g) The interval of time between the reduction divisions is affected by unseasonable high temperatures influencing the development of the sexual tissues..

With the facts deduced from the study of these species of Rhododendron taken in conjunction with the investigations carried out by other workers on various different plants, the writer of this paper arrived at the following general conclusions: -

In any hermaphrodite protandrous flower: -

(a) there is a definite interval of time normally elapsing between the male and female reduction divisions;

(b) the relation of the male and female reduction divisions in time has a determining effect on the sexual efficiency of the gametes;,

(c) this time relation may be altered by certain external conditions interacting with the inherent nature of the plant.