Neomeris dumetosa , L amour. 605 
on Acetabularia mediterranea ; here the young plant com- 
menced calcification before it became attached to the sub- 
stratum, and they suggest that a highly calcareous substratum 
is requisite for normal development. In view of the far 
greater deposit of lime in this species, it is evident that 
this must be the case, unless the energy of assimilation is 
correspondingly enormously increased. 
Finally, with regard to the mechanism of precipitation, it 
cannot be claimed that the case of Neomeris presents a solution 
of the problem. Pringsheim 1 has shown that a localization 
of calcification in species of Nitella is to be explained by local 
variations in the intensity of chlorophyll-assimilation ; and he 
regarded all phenomena of incrustation as being due solely to 
abstraction of carbonic acid from the surrounding medium 
containing calcium bicarbonate in solution, and consequent 
precipitation of carbonate on the surface of the plant. That 
water-plants can live healthily in such a solution, and can 
obtain carbonic acid for assimilation by decomposing the 
bicarbonate, and that the carbonate is precipitated on their 
surface, has been conclusively shown by Hassack 2 ; but only 
in a few cases did he succeed in obtaining a permanent 
incrustation, and hence falls back on the suggestion that there 
must be some peculiarity in the membrane of plants which 
normally calcify. Hassack, however, endeavours to show for 
Chara foetida , that the deposition may be referred to a preci- 
pitation of calcium carbonate outside the plant in consequence 
of the excretion of an alkaline carbonate, formed as a waste 
product in the assimilatory processes ; and Schimper 3 points 
out that such precipitation would present an analogy to the 
neutralization of acid potassium oxalate in the formation of 
secondary calcium oxalate. 
The chief difficulty with regard to such an hypothesis for all 
calcification is, as Pringsheim suggested, the explanation of 
the extremely localized deposit. It is not easy to see why 
an alkaline carbonate should be excreted in the immediate 
1 Jahrbiicher, vol. xix, p. 138. 2 Untersuchungen, Tubingen, III, p. 465. 
3 Flora, 1890, p. 239. 
