1895.] On the Weight of a Cubic Decimetre of Water. 143 



But, in the case of the Angiospermic anthers, we conclude, on com- 

 parative grounds, that progressive septation has taken place ; this 

 would indirectly support the view that the sorus of Dancea is also a 

 result of progressive septation. 



Obviously such a series of stages as that presented by Dancea may 

 be read either way, and it would be possible to urge that in them we 

 have evidence, not of progressive septation, but of fusion of loculi. 

 This question must be considered on grounds of general probability. 

 Without at the moment declaring a final opinion (though. I think the 

 probability is largely in favour of a view of progressive septation), 

 this point, at least, seems clear: that in Dancea the identity of the 

 sporangium or loculus is not strictly defined. To arrive at this point is, 

 in my opinion, a matter of some importance ; the study of the 

 sporangium in Pteridophyta has long been based upon the examina- 

 tion of the highly specialised and strictly constructed sporangium of 

 the Leptosporangiatse. The conclusion is, however, becoming obvious 

 that such strictness of construction and regularity of segmentation is 

 exceptional, and that in the Eusporangiatse such strictness is not the 

 rule. 



Other Marattiacese, and especially Kaulfussia, have also been 

 examined, and they are all found to conform to one fundamental 

 type, though differing in detail ; it appears that, as regards the sorus, 

 Dancea is the least specialised, and Angiojpteris the most specialised, of 

 the living genera, and that they form a very natural series. Such a 

 series in plants of so antique a stock deserves the most careful com- 

 parative study, and the results should carry unusual weight. 



III. " On the Weight of a Cubic Decimetre of Water at its 

 Maximum Density." By D. Mendeleeff, For. Mem. R.S. 

 Received October 16, 1895. 



The investigations of Sir Greorge Shuckburgh Evelyn, published in 

 the year 1798,* after allowing for the new measures made by Captain 

 Kater,t as well as for all corrections according to our present know- 

 ledge of the weight of a litre of air and on the expansion of water, 

 give the result that the weight of a cubic decimetre of water at its 

 maximum density (4° C.) in vacuo is equal to 1000*56 grams.^ But 

 in these investigations the separate determinations show differences of 



* « Phil. Trans.,' 1798, p. 133. 



f ' Phil. Trans.,' 1821, Part II, p. 316. 



X All these corrections are made in D. Mendeleeff's paper (in Russian) in the 

 VremenniTc (Bulletin) of the Central Chamber of Weights and Measures (Chambre 

 Centrale des Poids et Mesures), Part II, pp. 11 — 19. {Vide 'Journal of the Russian 

 Physico-Chemical Society,' 1895.) 



