350 Sex Characters in Begonias 



transmitted through the tissues which connect the ovule with the 

 mother plant. 



In the dioecious Lychnis if pollination and fertilization of the ovules 

 be prevented the female flower falls on the fifth or sixth day after 

 opening. This falling of the unfertilized flower (like the falling of the 

 autumn leaf) is brought about by a degenerative change in the collar 

 cells which form the neck of the floral peduncle at the point where this 

 swells out into the thalamus or cone on which the ovules are imbedded. 

 If on the other hand the ovules have been fertilized active growth 

 occurs in these cells. Either the absence of a stimulus derived from 

 the growing ovules or possibly the presence of an inhibitory sub.stance 

 formed by the atrophying and degenerating ovules brings about the 

 death and degeneration of these collar cells, and this results in the fall 

 of the unfertilized or insufficiently fertilized Hower. 



In the falling corolla after pollination, and the falling flower in the 

 absence of pollination, a quantitative relationship can be observed 

 between the number of pollen grains which gain access to the pistil 

 and the rapidity of the wilting of the stigma and corolla in the one 

 case, and the number of ovules which undergo fertilization and the 

 rapidity of the falling of the flower in the other. If only a few pollen 

 gi-ains are allowed to gain access to the pistil the petals may remain 

 erect and vigorous for several days, while if the stigmata be dusted with 

 a larger quantity of pollen they fall in 24 to 48 hours. In the case of 

 the flower, if only 5 or 6 ovules (in Lychnis) undergo fertilization the 

 degenerative change in the collar cells may not be prevented and the 

 flower may fall although it has been partly fertilized. A minimaJ 

 number of ovules must in fact undergo fertilization and begin to grow 

 in order to prevent those changes in the cells at the root of the thalamus 

 which lead to the falling of the unfertilized flower. 



This fjict, viz. that a quantitative relationship e.xists between the 

 factor which stimulates or arrests cell growth and the stimulated or 

 arrested cell activity which results from its influence is an important 

 one. It is unlike the behaviour of an animal enzyme which when 

 introduced into a fermentable solution serves to hydrolyse its whole 

 volume. 



It is also unlike the method of action of speciflc sex hormones, 

 where the .smallest quantity of the substance, if present in the blood 

 stream, is capable of influencing the metabolism of the whole body. 



In fact these chemical substances which stimulate and arrest cell 

 growth in plants seem to be incapable of self multiplication and seem 

 to exercise only a local influence on the tissues of the plant. 



