to the Plant Celt. 
529 
result of experiments in which sodium was added to solutions in which 
calcium was omitted, for there the lack of calcium seemed to be much less 
severely felt by the plants. 
The spores of Gymnogramme sulphur ea were able to germinate and 
produce normal prothalli in the absence of calcium salts. At the end 
of three months in the calcium-free solutions the prothalli were in good 
vegetative condition, and their meristematic cells contained a moderate 
amount of starch. The most striking variation from the normal course 
of development was found in the solutions where magnesium had been 
substituted for the missing calcium. The prothalli in these solutions had 
made very good growth, and had developed a very large number of 
antheridia, but no prothallus was ever found which had formed an arche- 
gonium. The cultures were continued for a total period of five months, 
during which time the prothalli in the control cultures developed both 
antheridia and archegonia, and, in course of time, young sporophytes. The 
prothalli in these calcium-free solutions did not, however, produce any 
archegonia. The antheridia which they produced were entirely normal, and 
produced normal antherozoids. 
It will be noted that these results have a similarity to those obtained 
by Prantl (’81) who cultivated fern prothalli on solutions lacking nitrogen. 
On nitrogen-free solutions he obtained only antheridia, but on complete 
nutrient solutions both antheridia and archegonia. The development of 
archegonia on the prothalli appeared to be closely related to the formation 
of meristematic cells. In the cases which I have studied, the appearance 
of archegonia did not seem to be necessarily conditioned by the development 
of meristem. 
It may be mentioned, in passing, that the nuclei of different sex cells 
of ferns differ, according to Zacharias (’87), in their chemical nature, and 
to this may be related the disappearance of one sort of cells under special 
conditions. The male sex cells are rich in nuclein and contain small 
nucleoli. The nuclei of the female sex cells are poor in nuclein, but rich 
in proteid and contain one or more nucleoli, often of large dimensions. 
There is an obvious correlation between the structure of the nucleus 
and its activity, chemical or otherwise. In an earlier paper (Reed ’04) 
I have shown that in the secreting cells of germinating seeds the nucleoli 
become smaller and the chromatin greater in amount as the activity of the 
cells increases. The observations there recorded indicate that the substance 
making up the chromatin and nucleoli is identical, the two forms differing 
mainly in their activity (or lability). Upon this hypothesis the nucleoli 
represent the less active or potential condition, while the chromatin 
represents the active or kinetic condition. Applying this theory to the 
case in hand, we may say that the active (kinetic) nuclei of the antherozoid- 
forming cells are able to obtain the materials from the incomplete solutions, 
