) 
Studies in Spore Development. 
III. The Premeiotic and Meiotic Nuclear Divisions of 
Equisetum arvense. 
BY 
RUDOLF BEER, B.Sc., F.L.S. 
With Plates LI-LIII. 
I N 1909 I published ( 1 ) a short account of the spore development of 
Equisetum with the principal object of recording the result of my 
observations upon the origin of the much disputed ‘ middle, coat ’ of the 
spore- wall. In contradiction to those who had written on this subject 
before, I found that this layer of the spore-membrane was derived from 
the secretory activity of the tapetal plasmodium which surrounds the 
developing spores. 
It had been my intention to publish a more detailed account of the 
spore development of this plant, but the appearance of a careful and thorough 
study of this subject by E. Hannigin 1911 ( 3 ) has rendered this unnecessary. 
Hannig, in his much more extensive memoir, has reached similar conclusions 
regarding the ‘ middle coat ’ (as well as in several other respects) to those 
to which I gave expression in my short note of 1909. 
The nuclear divisions associated with the spore development of 
Equisetum were, however, not dealt with by Hannig, and I thought that 
it might be of interest to describe these at greater length in the present 
communication. This seemed the more desirable since a fresh study of 
many new preparations has caused me to modify some of the views which 
I expressed upon this subject in my previous note. 
The material of Equisetum arvense (which was the only species used 
in this research) was collected in the autumn of 1908. A collection made 
on September 3 yielded sporangia, showing the various phases of the arche- 
sporial divisions. On September 8 and 9 the majority of the sporangia 
contained spore mother-cells in all stages of meiosis. On September 13 
the meiotic divisions had been completed in almost all the sporangia and 
were only occasionally met with, but the strobili showed all stages of spore 
development from the naked, membraneless spore to the spores of 38// 
diameter furnished with elaters. Later gatherings were made to complete 
[Annals of Botany, Vol. XXVII. No. CVIII. October, 1913 
X X 2 
