Ig10] SHATTUCK-—HETEROSPORY IN MARSILIA 39 
Fic. 3—Young sporangium, showing 8 of the 16 ana cells in synapsis, 
just as the tapetum begins to form the plasmodium. X29 
Fic. 4.—Older sporangium, showing tetrads with a tapetal plasmodium 
dispersed among them. X 292. 
1G. 5.—First stage in which one can determine that the sporangium is to 
contain megaspores; several spores are enlarging, but the mass of tapetal nuclei 
is collected about the larger one in the center. X 292. 
Fics. 6-10.—Showing the competition among the members of the tetrad and 
the persistence of the three aborting members through the various stages of 
megaspore formation; they are often evident even after germination, as shown 
in fig. roa. Figs. 6, 7, 8, 9, 300; rob, X 
PLATE IV 
Fic. 11.—Photomicrograph showing the aborted members of the tetrad stiN 
eee - the papilla of mature megaspore. X85. 
Fic. 12,—Diagrammatic representation of fruiting rhizomes, showing the 
effect of varying the depth of water when the plants are in such subdued light 
as to be just able to produce sporocarps; 6, blasting; m, maturing. 
Fic. 13.—Condition of various sporangia of a sorus during the process of 
blasting; a, old aborted microsporangium, megasporangium in the center; 8, c, 
ee es from same sorus. 
G. I4.—a, normal microsporangium; 6, sporangium in which the 16 mother 
cells sie not formed walls during the tetrad divisions; ¢, same in section; d, 
. Sporangium with extensive abortion, a few of the surviving spores enlarged. 
Fic. 15.—Portion of a section of a sporocarp in which all the megaspores 
have aborted, as shown by the empty megasporangia, m; in the microsporangia 
no walls have been formed in the tetrad divisions, so that each sporangium con- 
tains but 16 enlarged and irregular bodies instead of the usual number of 64 
spherical spores. ss. 
Fics. 16, 17. —Single entire sporangia, showing the 16 bodies as in jigs. 14), 
and 15. X10 os. 
Fic. 18.—Three sections, a, }, c, of various bees from sporangia as in 
figs. 16, 1 7, showing nuclear structure and behavior. X400. 
PLATE V 
Fics. 19, 20.—Similar to fig. 18; forms more irregular. X 400. 
1G. 21.—Microspores resulting fron tetrads which have had varying success 
in forming ace during the second division, due to unfavorable conditions of 
growth. X13 
Fic. 2 Naclead structure and behavior in earlier stages of such micro- 
Spores. X 400. 
Fic. 23.—A normal microsporangium at maturity, containing 64 spores. X95. 
Fics. 24, 25.—Microsporangia in. which many of the microspores have 
