Grtnnellia americana, Harv. 13 



originate and develop by apical growth : ' An diesem Thallus 

 entstehen die Sexualzellen durch Differenzirung einzelner 

 Endzellen des ganzen Systems verzweigter Zellfaden.' 



Grinnellia americana 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. 



B4 



