Grinnellici omericana , Harv. 13 
originate and develop by apical growth : ‘ An diesem Thallus 
entstehen die Sexualzellen durch Differenzirung einzelner 
Endzellen des ganzen Systems verzweigter Zellfaden.’ 
Grinnellia americanct seemed an exception to Schmitz’s 
law of development, because of the patches of antheridia and 
the cone-shaped conceptacles which originate from the mem- 
branaceous male and female fronds. Dr. Schmitz does not 
mention this peculiar Alga, which was probably inaccessible 
to him. To prove, therefore, whether this genus is an 
apparent or a real exception to his law, made the study of 
its development exceedingly interesting. 
In the development of the antheridia, individual vegetative 
cells in different parts of the frond are observed to change 
from a pronounced red to a lighter colour, possibly due to 
an accompanying development of a large amount of granular 
matter of a highly refractive character. Similar changes are 
observed to follow immediately in many of the cells adjoining 
these centres, causing the male fronds to be patched promis- 
cuously on both sides with numerous collections of these 
lighter-coloured granular cells. These individual groups 
occupy irregular areas varying from two to twenty times the 
surface of the average vegetative cell, and are covered with 
a thicker gelatinous layer than the vegetative portion of the 
frond (Fig. 9). Cross-sections of these regions show that the 
significance of the excessive granular substance in this instance 
is the modification of vegetative tissue in preparation for the 
formation of reproductive elements. The sections were 
prepared from antheridial fronds which had been stained 
two hours in Delafield’s haematoxylin. They show that the 
modified vegetative cells divide transversely, and that each of 
the daughter-cells repeats the process at both ends, in a plane 
at right angles to the first plane of division, thus giving rise 
to three layers of cells instead of one (Fig. 8). 
The protoplasm of the cells last formed collects into a dense 
mass at the distal end and forms a spherical body, which 
separates by a constriction of the cell-wall below it. (Fig. 
8 d, d' c. c .) The spherical cell thus formed is an antherozoid. 
