1903] GAMETOPHYVTES AND EMBRYO OF TAXODIUM 21 
first cell walls in the young gametophyte is shown in fig. 24, and 
I can confirm Mlle. Sokolowa’s observation, also recently 
repeated by Ikeno (’98) and Arnoldi (’00), that the inner sides 
of the first cells are open. Mlle. Sokolowa gives the name 
“alveoli” to the ingrowing tubular cells of the prothallium, but 
this term does not seem to have much to recommend it. It is 
repeated by Arnoldi (’00) in his work on Sequoia. 
In view of the supposed relationship | of Taxodium and 
Sequoia, it is of interest to compare the endosperm-formation 
in the two cases. Arnoldi has described in some detail a 
double process in Sequoia which he considers to have signif- 
cance from the phylogenetic point of view. The prothallial 
region which is to bear the archegonia is formed in the usual 
way by ingrowing open tubes, which finally meet in the center. 
This area may be either in the center of the sac alone, or may 
extend entirely to the tip. In the latter case, however, Arnoldi 
considers the tip to be lacking. The tissue at the tip does not 
form in the usual way, but it is produced by free cell-formation, 
as in the endosperm of angiosperms. This free cell-formation 
begins in the tips before the tubes appear in the archegonial 
region. In Taxodium, on the contrary, cell-formation usually 
begins earlier at the tip, where archegonia are to appear, than at 
the base of the prothallium, and firm cell walls are frequently 
lacking in the lower parts long after they have been established 
in the upper. In fact, cases are not infrequent in which the 
lower part of the gametophyte is in an embryonic condition, 
€ven after fertilization has occurred in the archegonia. In some 
cases, however, firm cell walls seem to be formed almost simul- 
taneously throughout the spore. In the upper part of the 
prothallium it is-always easy to see that cell-formation has 
Proceeded by the usual growing-in method. 
Fig. 55 shows prothallial tubes from near the tip of the sac 
after their closure on the inner side. (Mlle. Sokolowa [90 | 
has shown that the closure occurs when the inner ends of the 
tubes meet in the center.) ig. 56 shows the first division of a 
Prothallial tube and the preparation for the second. By these 
divisions there are formed rows of cells radiating from the 
