172 Trow . — Observations on the Biology and 
attractive power in spores which has the property of con- 
verting them into fusing gametes. This unfortunately does 
not get rid of all the difficulties ; for although the reducing 
division in sporogenesis is now readily explained by reference 
to atavistic phenomena, the case of Fncus can receive no 
valid explanation without regarding the plant-body as a 
sporophyte. One sudden development is as difficult to 
explain as another. A sudden evolution of attractive power 
is as difficult to understand as the sudden evolution of reduced 
nuclei. Moreover, it is always easier and better to explain 
the complex by the simple, the Lily by the Wrack, than 
vice versa. The gradual displacement theory, too, of Stras- 
burger, is difficult, if not impossible, to conceive in detail. 
How, for example, is the boundary between the two gene- 
rations to be crossed? 
I venture to bring forward tentatively a view which appears 
to me to meet the case, and which in a less complete form 
appeared in the Annals of Botany three years ago. It appears 
to be certain that the number of chromosomes in the nuclei 
of an individual plant may be variable, as variable indeed 
at times as any other morphological character of a plant. 
The work of Dixon (’94) on Pinus silvestris 1 may be cited 
in support of this. We may further grant with Strasburger 
that a gamete becomes such by the development, very gradual 
probably, of a mutual attraction for other gametes. The 
behaviour of highly developed sexual gametes may be easily 
explained on such a hypothesis. When the ancestral asexual 
plants commenced to acquire sexual characters there was no 
hard and fast line between gametes and spores, and that is 
1 Blackman’s (’98) results, indeed, may be brought forward to throw discredit 
upon Dixon’s work. The vacillation of so expert and experienced an observer 
as Strasburger, however, and the careful figures and very positive statements of 
Dixon, must have some foundation in fact. That fact may well be the variability of 
the number of chromosomes in different individuals. Blackman’s negative evidence 
has consequently little weight. It may further be noted that in the well-known 
Lilium Martagon the number of chromosomes is subject to variations, as was 
very clearly shown by Guignard. Moreover, nothing is more patent, in the records 
of recent research, than the uncertainty with which botanists declare their results 
as to countings of chromosomes. 
