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 generatioti. It is evident, indeed, 

 that they 7mist vary greatly, according to whether each one has 

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

 number of both, fropi 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 Pisuni, Phaseolns, 

 Lactuca, Tragopagon, and Datnra, mentioning especially in this 

 connection the hybrid of Nicotiana alata and A^. la^igsdorffii. 

 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. 



