300 THE GERM-PLASM 



cestral species. If therefore the ' reducing division ' halves the 

 germ-plasm of these mother-cells in such a manner that idants 

 of the mother alone reach one ripe germ-cell, and those of the 

 father alone are contained in another, it is possible that two such 

 germ-cells may unite when fertilisation takes place between 

 these hybrids. In such a case a plant completely resembling 

 one of the ancestral forms would arise, for it would have been 

 produced from a germ-plasm which contains idants of this species 

 only. As however such cases do not often occur, we may con- 

 clude that the reducing division only rarely effects such a com- 

 plete separation of the paternal and maternal groups of idants, 

 and that, in fact, as a rule, both paternal and maternal idants 

 are distributed to each of the four germ-cells produced by the 

 mother-germ-cell. As this halving of the germ-plasm occurs, as 

 we have seen, in a different manner in different instances, we 

 may presuppose that it will also exhibit differences with regard 

 to the proportion of paternal and maternal idants which come 

 together in each germ-cell in consequence of the reducing 

 division ; and this supposition is most satisfactorily borne out 

 by the facts, for it is well-known that the offspring of hybrid- 

 plants, produced by fertilisation with their own pollen, become 

 very variable in the following generation. It is evident, indeed, 

 that they must vary greatly, according to whether each one has 

 received a greater number of maternal or paternal ids, or an equal 

 number of both, from the two germ-cells which combined in 

 the process of fertilisation to produce this particular individual. 

 Thus Focke describes the offspring of hybrid-plants of the first 

 or second year as being ' as a rule unusually diverse and rich 

 in forms,' and gives as examples the genera Pisiim, Phaseolus, 

 Lactiica, Tragopagon, and Datura, mentioning especially in this 

 connection the hybrid of Nicotiana alata and N. langsdorffii. 

 De Vries * also refers to these facts, and describes them very 

 aptly in the following passage : — • The hybrids of the first gen- 

 eration have perfectly distinct characteristics in the case of 

 every pair of species. If a hybrid is produced from two species 

 which have already been crossed successfully by previous ex- 

 perimenters, we may be sure that the description given by 

 them will as a rule apply exactly to the intermediate form in 

 question. If the hybrid is fertile without the help of the parent- 



* Hugo de Vries, ' Intracellulare Pangenesis," Jena, 1889, p. 25. 



