186 M. C. Stopes. 
The reduction division, though similar in its main features to 
those of the higher plants, has some characters peculiar to itself. 
Among these is the fact that the spirem and the synapsis are very 
precocious, appearing while the tetrasporangium is still very small. 
After the longitudinal splitting of the thread there is a long period 
of growth of the cell during which the nucleus is apparently in the 
resting condition and the spirem as such has completely disappeared. 
In the prophase proper the sixteen chromosomes appear as 
long rods bent over so that their limbs are parallel, or cross each 
other, or meet so as to form closed loops. Detailed descriptions 
with figures are given in a paper shortly to appear in the Annals of 
Botany ; here it only remains to add that the only explanation that 
seems to account satisfactorily for the facts is that suggested by 
Farmer and Moore, in their paper recently read before the Royal 
Society 1 in explanation of the phenomena of reduction in several 
plants and animals. According to this each chromosome is bivalent 
and only once split. The two arms of a looped figure would then 
represent two chromosomes, and the two are separated from each 
other by a transverse division during the metaphase of the succeeding 
mitosis, thus bringing about true reduction. 
1 Proc. Roy. Soc., Vol. 71, 1903. J. LLOYD WILLIAMS, 
Assistant Lecturer in Botany , 
September , 1903. North Wales University College. 
THE COLONISATION OF A DRIED RIVER-BED. 
By Marie C. Stopes, B.Sc. * 
(Read before Section K of the British Association at Southport). 
I N the past the little river known as the Ebbsfleet, which ran from 
Southfleet to the Thames, just to the west of Northfleet, 
Kent, has had some influence on the history of the country. At 
its source was situated the Roman settlement of Vagniaci, and its 
presence interrupted the straight course of Watling Street. The 
stream was a stopping place for the pilgrims going to Canterbury in 
Chaucer’s time, and there is proof that as late as Elizabeth’s reign 
it was tidal, and of sufficient size for considerable ships to anchor 
on its course. This proves that the stream has a consecutive 
history of many centuries at least, but three years ago its water 
was abruptly and completely removed, thus leaving the water-loving 
plants suddenly exposed to dry conditions. 
This is not the same, cecologically, as the slow drying up of pond 
or stream where the plants retreat generation after generation, and 
as I am unaware that any similar case has been treated botanically 
