342 Some Notes on Azolla. [zoe 



In the macrosporangium but eight spore mother cells are produced, 

 while in the microsporangium there are sixteen. In both cases, each 

 spore mother cell divides into four, in the usual way; but whereas all 

 of these develop more or less perfectly in the microsporangium, only 

 one comes to maturity in the macrosporangium, and develops into 

 the single large spore that fills its cavity. 



Shortly before maturity the protoplasmic matter filling the micro- 

 sporangium separates into several masses (massulas) each of which 

 encloses a number of spores. The substance of the mature massulae 

 has a peculiar foamy appearance, and looks almost like a cellular tis- 

 sue, but examination shows that it is only hardened protoplastic mat- 

 ter, and that the peculiar cellular appearance is caused by vacuoles 

 in it. In stained sections of the nearly ripe sporangium, the nuclei 

 of the disorganized tapetal cells can still be seen lying in the spaces 

 between the massulae, and are evidently concerned in the formation 

 of the glochidia, curious anchor-like outgrowths of the massulae. 



In the macrosporangium the protoplasmic matter surrounding the 

 spore is used to build up the curious epispore and appendages. The 

 epispore in AzolLa filiculoides is composed of a substance very similar 

 to that of the massulae. It is provided with prominent irregular 

 knobs that have attached to them numerous fine threads. The up- 

 per part of the spore is crowned with three pear-shaped masses of 

 the same substance as the epispore. The ripe macrospore fills the 

 sporangium so completely, and the latter fits so closely into the in- 

 dusium, that its wall is so compressed as to be only discernible after 

 close scrutiny. 



The sporangia are set free by the decay of the indusium, but this 

 decay is only partial in the case of the macrosporangium, and the 

 upper part of the indusium becomes hard and dark-colored, and per- 

 sists as a little cap, covering the top of the spore, whose base finally 

 becomes entirely free by the decay of the sporangium wall. As the 

 massulae escape from the microsporangium, by the complete disor- 

 ganization of its wall, the glochidia stand out from them and by 

 their hooked ends become fastened to the threads that cover the 

 prominences on the surface of the macrospore, and often the massu- 

 lae are so numerous as to completely hide the lower part of the ma- 

 crospore. This is obviously a great assistance in fertilization, as the 

 germinating microspores are thus brought close to the macrospore. 



In order to study the germination of the spores, sections must be 



