COMPLEX REPRODUCTION 441 



of the organism, so that this method of reproduction need not be 

 described as apomixis. 



For simpHcity the different abnormaUties of reproduction have 

 so far been considered separately, but in their occurrence they are 

 not easily separable. It is common for apomictically reproducing 

 plants to show several abnormalities together. This is particularly 

 well exemplified by Artemisia nitida (Chiarugi, 1926). This triploid 

 species is sexually sterile and its normally produced megaspores die, 

 their place being taken by aposporous embryo-sacs. Failure of 

 reduction gives diploid parthenogenesis, so that seed may develop 

 in two ways and in three other ways may fail to develop (Table 68) . 

 One ovule may contain several mother-cells and show all these 

 variations side by side. In Ochna serriilata, a different complication 

 arises : the differentiation of tissues in the ovule is not always 

 clear, so that the distinction«between parthenogenesis and apospory 

 fades away. 



Which of these different types of reproduction can be successful 

 is probably decided by competition. Clearly the haploid or 

 irregularly reduced embryo-sac of a hybrid will stand little chance 

 against the somatic embryos. Where numerical reduction has 

 failed the odds will be reversed. This competition has been well 

 illustrated by Haberlandt (1921 h) in Hieracium flagellare. Such 

 competition is perhaps characteristic of all stages of development of 

 gametophytes and embryos in hybrids, as in (Enothera. 



A different range of abnormality is found in Allium odorum 

 according to Modilewski (1930). The egg-cell develops in one of 

 four ways : (i) normally, after reduction and double fertilisation ; 

 (ii) after failure of reduction with fertiHsation of the fusion nucleus 

 only, so that the embryo is diploid, the endosperm pentaploid, as in 

 Zephyranthes ; (iii) after failure of reduction but without 

 fertilisation of the fusion nucleus ; (iv) by haploid parthenogenesis. 

 The last two processes result in degeneration at an early stage : 

 fertilisation, single or double, is indispensable. 



(iv) Lower Organisms (Thallophyta and Protista). Amongst the 

 lower organisms alone is found the type of reproduction in which 

 meiosis immediately follows fertilisation, and is perhaps immediately 

 conditioned by it (D., 1932). In these we find both diploid par- 



