Azolla filiculoides , Lam. 165 
respects, especially in the later stages. While the macro- 
sporangium has a very short massive pedicel, that of the 
microsporangium is long and slender, usually composed of 
two rows of cells, but not infrequently showing three. Up to 
the third division of the central cell of the sporangium the 
divisions are exactly as in the macrosporangium ; but in the 
microsporangium there is one more division and consequently 
sixteen spore-mother-cells. The sixty-four spores that result 
from the division of these, all develop more or less completely, 
and about each is formed a smooth, thin, yellowish exospore. 
The ripe spore is about ‘035mm. in diameter, and its apex 
shows plainly the usual three radiating lines. The full-grown 
microsporangium (Fig. 26) is globular, its walls formed of 
tabular cells all about alike. I was unable to detect anything 
that looked like the annulus of the homosporous leptospor- 
angiate Ferns. The complete disappearance of the annulus is 
no doubt attributable to the aquatic habit of Azolla . 
When the spores are nearly mature, the formation of the 
massulae or masses of hardened protoplasmic matter in which 
the ripe spores are imbedded, begins. The spores collect in 
several groups (usually about five), and about these the pro- 
toplasm lying between them becomes aggregated. Apparently 
vacuoles are formed in this giving it a foamy appearance, and 
finally these become so large as to give the massula the 
appearance of a cellular tissue (Figs. 24, 27, 28). In Salvinia , 
where there is no division into massulae, according to 
Strasburger s 1 account, the nuclei of the tapetal cells are 
scattered uniformly through the protoplasm lying between 
the spores ; but in Azolla , they are confined to the outside of 
the massulae, where they can be readily detected almost up to 
the time of the ripening of the sporangium. As the massulae 
mature there are formed upon the outside the glochidia, curious 
hair-like appendages with anchor-like tips. They are formed 
in the spaces between the massulae, and their flattened form 
is due to the narrowness of these spaces. The presence of 
the unchanged tapetal nuclei about the forming glochidia 
1 Bau und Wachsthum der Zellhaute, p. 133. 
