XI LEPTOSPORANGIATM HETEROSPOREM 429 



food from the spore. The volume of the protoplasm in the 

 spore increases as the prothallium grows, but loses more and 

 more its coarsely granular structure. In both Marsilia and 

 Pilularia the nucleus of the spore cavity soon becomes indis- 

 tinguishable, and in the former is from the first very small. In 

 Pilularia it is larger, and in the later stages bodies were ob- 

 served that looked as if they might be secondary "endosperm- 

 nuclei," like those of Azolla, but their nature was doubtful. A 

 further study of Marsilia vestita has shown irregular deeply 

 staining bodies in the protoplasm below the basal prothallial 

 cells, which may perhaps be nuclei like those described by Coker 

 ( I ) in M. Drummondii. 



The early leaves are at first alike in both genera, and the 

 earliest ones do not show any trace of the circinate vernation of 

 the later ones. In Pilularia the later leaves are essentially like 

 the cotyledon, but in Marsilia all the later leaves show a distinct 

 lamina. This is at first narrow and undivided, and spatulate 

 in form. In M. vestita this is succeeded by five or six similar 

 ones, with constantly broadening laminae, which finally divide 

 into two narrow wedge-shaped lobes, and these are then suc- 

 ceeded by others with broader lobes, which finally are replaced 

 by four lobes, the central ones being narrower than the outer 

 ones. All of these early lobed leaves are folded flat, and it is 

 not until about ten or twelve leaves have been formed that 

 finally the leaf attains the form and vernation of the fully-devel- 

 oped ones. 



The divisions in the stem apex take place slowly, but appar- 

 ently a complete series of segments is produced in rapid succes- 

 sion, and there is an interval before any more divisions occur, 

 as there is always considerable difference in the ages of any 

 two succeeding sets of segments. The apical cell of Pilularia 

 in cross-section has the form of an isosceles triangle with the 

 shorter face below. Probably each dorsal segment at first 

 gives rise to a leaf, and each ventral one to a root. However, 

 the number of roots exceeds that of the leaves, but the origin 

 of these secondary roots was not further investigated. 



The Mature Sporophyte 



In both Marsilia and Pilularia the fully-developed sporo- 

 phyte is a creeping slender rhizome, showing distinct nodes and 



