Beer, Development of tlie pollen grain and anther of some Onagraceae. 295 
from ab out 40 to 45 t u tbe protoplast still completely fills the 
cell-cavity but it has become entirely free from its walls. 
Tlie further increase in the size of the pollen grain which 
now takes place is more rapid than that of the living protoplast 
which consequently no longer fills the cell - cavity (Fig. 24). 
AVe have here, in fact, conditions which strikingly recall those 
which Fitting and others 1_4 ) have described in the case of the 
megaspores of Lsoetes and Selaginella. 
These results have such an important bearing upon our 
conceptions of the growth of vegetable membranes and render 
some features of this process so difficult to understand that 
several botanists have hesitated to accept them until they could 
be placed upon a broader basis them was done by those who 
have examined the megaspores of the Lycopodiales. 
AAuth the exception of Fitting, these authors have exclu- 
sively rested their conclusions upon microtome sections. Invalu- 
able as such sections are we must not overlook the fact that 
the long series of manipulations necessary for killing, fixing and 
embedding in paraffin introduce many possible sources of error 
and the results obtained by this means should be carefully 
checked by observations upon living material. 
Fitting worked largely with living spores which he exami¬ 
ned partly in pliysiological salt solution and partly in water. 
Fnfortunalely he gives us no details of liis methods and it 
would be very desirable to know exactly what was the strength 
of his pliysiological salt solution and wliether this particular 
concentration was found by direct experiment to produce less 
change in the cell than any other strength. His selection of 
water as an alternative medium in which to examine the con¬ 
dition of the protoplast was most unitable as water is known 
to affect the protoplasm and its osmotic condition. 
The pollen grains of Oenothera are particularly favourable 
for investigation and I liave attempted to make my examination 
of them as complete as possible. Fresh material has been exa¬ 
mined in the first place and the results thus obtained have been 
compared with microtome sections of material fixed with strong 
and weak Flemming's 'Solutions, with strong and medium 
chrom-acetic solution * 2 3 4 5 ), Merkel‘s fluid and AYorcester’s fluid 6 ). 
4 ) Fitting, FL, „Bau und. Entwickelungsgeschichte der Alakrosporen 
von lsoetes und Selaginella etc.“ (Bot. Zeit. Bd. 58. 1900. pp. 107—164.) 
2 ) Denke, P., „Sporenentwickelung bei Selaginella'''-. (Beihefte z. Bot. 
Centr. Bd. XII. 1902. p. 182.) 
3 ) Lyon, AL F., „A study of the Sporangia and G-ametophytes of Sela¬ 
ginella Apus and S. Rupestris u . (Bot. Gazette AA1. XXXII. August-Sep¬ 
tember 1901. pp. 124—141 and pp. 170—194.) 
4 ) Campbell, FL D., „Studies on the Gametophyte of Selaginella “. 
(Annals of Bot. Vol. X\ T I. 1902. pp. 419—428.) 
5 ) Formulae in Chamberlains „Alethods in Plant. Histology“ p. 28. 
6 ) Formula for this fluid was obtained from FL S. Peeds paper upon 
enzyme secreting cells of Zea and Phoenix. (Ann. Bot. April 1904. p. 271.) 
20* 
