MARSILIA VESTITA. 187 



to determine with great precision every step in the forma- 

 tion of the prothaUium and embryo. 



THE MICROSPORES AND MALE PROTHALLIUM. 



The microspores of M. vestita are globular cells about 

 .075 mm, in diameter. The outer wall is white and suf- 

 ficientl}' transparent to allow the contents of the spore to 

 be dimly seen through it. Its surface presents a punctate 

 appearance, and at one point there are three lines which 

 meet each other at equal angles and mark where the 

 spore was in contact with its three sister-spores in the 

 mother-cell (pi. iii, fig. 3). Lying close to the inner sur- 

 face of the wall may be clearly seen numerous distinct 

 starch granules, and in the center the nucleus is vaguely 

 discernible ; covering the outside of the spore is a thin 

 structureless mucilaginous la3^er, which, however, is scarce- 

 ly perceptible in microtome sections. 



Sections through the ungerminated spore show that the 

 wall is thick and has several distinct layers. The inner- 

 most is thin and delicate, and is probably composed of 

 cellulose. The second is thicker and more or less cuti- 

 cularized, and the outer wall (epispore) is thick and ap- 

 parently composed of prismatic rods placed close to- 

 gether (pi. Ill, figs. 5 and 6). A surface view of the 

 epispore shows that it is the ends of these prismatic rods 

 that give the punctate appearance already noted. This 

 outer coat may be easily removed by mounting the fresh 

 spores in a drop of water and covering with the ordinary 

 cover glass, which is then rubbed carefully to and fro. 

 The smooth, colorless and semi-transparent exospore is 

 then seen, but it is not possible to get a satisfactory view 

 of the interior of spores thus treated. In the later stages 

 by boiling upon the slide, especially if a little potash is 

 added to the water, the exospore may be ruptured, and 



