ARREST 57 



that in Artanthc jamaicensis, one of the Piperaceae, only the posterior 

 stamen of the inner staminal whorl is formed, but it is larger than the 

 three stamens of the outer whorl ; in some flowers however this posterior 

 stamen only appears as a protuberance and does not reach complete 

 development and is apparently absent ; sometimes the first laying down 

 of such a protuberance is suppressed even to the first cell-divisions, and 

 therefore the formation of such a member can only be concluded from 

 other circumstances l . 



It is not always easy to separate arrested organs from those which 

 are transformed and from those which experience only a temporary 

 retardation of their development. The leaves, for example, on the rapidly 

 growing shoot-axes of many climbing plants remain at first in an un- 

 developed condition, and are either thrown off in this state or resume later 

 their development. The ' resting buds ' of many trees become arrested 

 when they are not called upon to sprout through an injury to the tree. 



The examples which have been already briefly referred to show that 

 the arrest may take place earlier or later in one and the same organ, and 

 consequently the construction of arrested organs varies in an extraordinary 

 degree. Examples from the vegetative region as well as from the flower- 

 region can be easily found. The lowermost glume of the spikelet of 

 Lolium is in most cases suppressed, but in Lolium temulentum its 

 presence can always be proved in development, and it often reaches such 

 a size that it is visible to the naked eye. The bracts of the flowers of 

 Cruciferae are usually suppressed, but sometimes they appear. Arrested 

 stamens show all intermediate stages from the normal structure of the 

 anther to an unsegmented papilla 2 . It is quite characteristic of many 

 flowers with greatly developed corollas that the stamens experience a 

 very early retardation of their growth, which does not occur in so great 

 a degree in the carpels which follow them ; the ray-florets of many 

 Compositae supply illustrations. Carpels and ovules also show all stages 

 of arrest. Organs in a condition of arrest usually appear somewhat later 

 than their position would warrant, and if it should happen that there is 

 no trace of the organs at all then the very spot on which they ought 

 to stand may disappear. Thus, for example, the flower of Labiatae is 

 typically pentamerous, but the development, from the formation of the 

 corolla inwards, is quite that of a tetramery. 



1 Schmitz has introduced the term ' Ablasty ' for the suppression of all trace of an organ in contra- 

 distinction to ' Abortus.' As has been stated in the text, there is no essential difference between the 

 two processes ; the assumption that an organ has disappeared can only be determined by com- 

 parative investigation. The circumstance that in such comparisons mistakes are sometimes made 

 cannot be regarded as an obstacle. [See note I on preceding page. ' Ablasty ' is the equivalent of 

 Suppression.'] 



2 



Familler, Biogenetische Untersuchungen, in Flora, iS^O, p. 133 



