104 Morphology BOOKI 



ture in the prothallus, of which he held it to be a part, whose 

 formation, taking place after fertilization of the oosphere, 

 is due to a resumption of vegetative activity by a certain 

 constituent of the primary prothallium under the stimulus 

 of the fertilizing fusion. Such resumption of vegetative 

 activity is illustrated in other directions, particularly by the 

 carpellary structures, causing them to develop into the fruit. 

 Another view of the formation, however, was advanced 

 in 1887, by Le Monnier, long before Nawaschin's discovery. 

 He suggested that the polar nuclei are both sexual, and 

 that their fusion is comparable to that of the gamete of 

 the pollen tube with the oosphere. In consequence of 

 this fusion he held that a second embryo is developed, 

 and that polyembryony is the normal state of things in 

 the embryo-sac. As usual, in cases of polyembryony, only 

 one embryo matures, and Le Monnier suggested that the 

 second was from a very early stage modified for physio- 

 logical reasons, in fact, was altogether subservient to the 

 nutrition of the first. 



Nawaschin's discovery brought Le Monnier's theory again 

 into prominence. It was supported in 1900 by Miss 

 Sargant, who suggested that the reason for its abnormal 

 development is perhaps to be looked for in the fact that 

 the antipodal polar nucleus is a vegetative and not a sexual 

 structure, and hence not unlikely to cause an abnormal 

 development. An argument in favour of the process 

 being one of sexual fusion is derived from the observations 

 on xenia which have been made by various writers since 

 1860. Xenia may be defined as an effect produced on 

 the endosperm in consequence of fertilization by alien 

 pollen, and is consequently noticeable in connexion with 

 hybridization. It implies that the endosperm shows the 

 characteristic features, not only of the plant in which it 

 is formed, but also of that from which was derived the 

 pollen the pistil received. It was first noticed by Hilde- 



