3 1 o Ward . — On Relations between Host and Parasite 
large scale I think average results of value could be obtained 
and tested. 
14. Stomata. 
I have elsewhere 1 published the details of my examination 
of the stomata, showing that there is no discoverable relation 
between their sizes and numbers, and may refer to that 
demonstration for information as to the methods of estimation 
and of checking pursued. It was natural to expect that, 
since the germ-tubes enter the leaves via the stomata, the 
sizes and numbers of the latter would be important factors : 
on the contrary, they seem to be of no importance whatever 
in connexion with the question here raised. 
15. Hairs. 
It is conceivable that the degree of hairiness of the leaf 
may be a factor in hindering the access of the germ-tubes to 
the stomata. In any case I found that in certain series of 
experiments where spores were kept in place on the leaves by 
fluffy masses of cotton-wool, the germ-tubes frequently ran 
into the interstices and appeared to lose themselves there 
instead of finding their way to the stomata. Too much 
stress must not be laid on these observations, however, since 
such wet pads of cotton-wool may have altered the conditions 
considerably — e. g., impeding access of oxygen, light, gas 
interchange and so on — and it is probable that the natural 
hairs never become thoroughly wetted as were these saturated 
cotton fibres. 
Be this as it may, it seemed worth while to obtain measure- 
ments of the length and the relative numbers of the hairs, 
and the results — obtained simultaneously with those of the 
stomata and hence by similar methods — are set forth in 
Table XXIV. 
The columns explain themselves. In column 1, in addition 
to the extreme lengths, I have added the commonest averages. 
1 Proceedings of the Cambridge Philosophical Society, vol. xi, Part V (1902), 
pp. 318-323. 
