a 
1906] LEWIS—DEVELOPMENT OF RICCIA 133 
water; therefore the ground form is not sterile, as was the opinion 
of LINDBERG and GARBER. 
4. Plants which have been growing attached to the soil and have 
been submerged by the filling up of the ponds do not necessarily 
perish, but are adapted to spend the winter under water and then 
to break loose by the decay of the older part of the thallus and float 
upon the water in the spring. 
5. The plants are propagated vegetatively by the separation of 
branches of the thallus, by the decay of the older part, and also by 
the growth of new plants from cells in the apical region. 
6. The sexual organs and fruit of the two species studied agree 
in their development with the accounts given for the other species 
of Riccia. There is no rudimentary integument surrounding the 
archegonium or sporophyte of Riccia natans. The sporogonium 
of Riccia natans is larger than that of Riccia crystallina and produces 
a larger number of spores. The only sterile tissue in either is the 
amphithecium, a single layer of tabular cells surrounding the mass 
of spore mother-cells. 
7- Centrosomes are not present in cells outside the antheridium 
nor would I interpret any structure observed in the cells of the 5 eee 
phyte or the spore mother-cells as a centrosphere. 
8. Bodies which resemble centrosomes, and which are con- 
sidered to be true centrosomes by certain authors, occur in the cells 
of the antheridium. These bodies do not have genetic’ continuity, 
but arise de novo with each division. They do not disappear after 
the last division of antheridial cells but remain in the spermatids 
and later become blepharoplasts. 
9. In the earlier divisions of cells in the antheridium, the spindle 
is arranged parallel to the long axis of the cell, but in the last division, 
the spindle is placed diagonally in the cell. No wall is formed 
between the two cells produced by this division, each of which becomes 
a spermatozoid. Thus two sperms are produced from each cuboidal 
cell. , 
10. In the developing sperm, the blepharoplast takes a position 
on the membrane of the cell and the two cilia grow from it, the nucleus 
becomes almost homogeneous in structure and _ crescent-shaped, 
almost enclosing the cytoplasm. The mature sperm consists of the 
