202 JOURNAL OF THE PLYMOUTH INSTITUTION. 
inappreciable quantity. I give the conclusion in the author's own 
words: "Now if we suppose that as the method is only an 
approximate one, the errors are entirely on one side, which I 
know no reason for doing, and therefore in round numbers reduce 
this fraction to the one two hundred -thousandth of an inch, it 
nevertheless provides us with a fact of much interest, and indicates, 
as I believe, that an atom of semi-transparent structure, the one 
two hundred -thousandth of an inch, may become visible under 
proper conditions of illumination and general manipulation. How 
far this is the actual limit with transparent or nearly transparent 
objects I will not venture to affirm, but I am inclined to believe 
that it comes very near to it." 
The interesting relations existing between flowers and insects are 
well known to all, thanks to the observations of Darwin and others, 
and the popular book of Sir John Lubbock ; but the first record 
of a possible participation of animals in the fertilization of crypto- 
gams has just been made by Dr. Dodel-Port, a Swiss botanist.* 
In almost all non-agamic cryptogams the contents of the male 
cells are actively moveable, and when they quit the cells they 
move about freely in the water by means of the cilia attached to 
them, and so reach cells of the female plant, and fertilization is 
completed. " In the case of phanerogams, the independent mobility 
of the pollen bodies has become an impossibility. To effect the 
union of pollen grains with that particular part destined to receive 
them, in most plants, some external agent must interfere. In many 
cases, especially in the lower regions of the floral world, the wind, 
gravitation, or both together, are the agents in question ; in the 
majority of the higher phanerogams, insects, or occasionally other 
animals, undertake the conveyance of the pollen. Now there are 
a great number of cryptogams in which the contents of the male 
cells, which are emptied into the water, do not possess the faculty of 
independent motion, as they are not endowed with cilia, and are 
therefore dependent upon the action of external forces for their 
locomotion. To these belongs the great and highly differentiated 
order of so-called red seaweeds or Florideae, chiefly marine plants 
which vary much in form and colour, and which no one who has 
ever attentively observed on the sea coast will ever forget. Their 
antherozoids, which are generally spherical, are discharged into the 
water as motionless cells, and are yielded up to the play of currents 
* Nature, vol. xx. p. 463. 
