VOL. III.] Sorne Notes on Azolla. 341 



gations will be given here, as the details will be given in a somewhat 

 extended paper that has just been completed. 



The plants multiply very rapidly by the djetachment of branches 

 at the base, which become independent plants, and in this way the 

 plant spreads with great rapidity when once established. Besides 

 this method of multiplication, spores are formed which give rise to 

 a new generation of plants. 



The spores are of two kinds, large ones (macrospores), and small 

 ones (microspores). The sporangea that contain these are borne in 

 separate receptacles, which usually occur in pairs. These are borne 

 on the lowest leaf of a branch, and an investigation of their earlier 

 stages shows that they are metamorphosed leaf-segments. The or- 

 dinary leaves are divided almost to the base, into two lobes, and in 

 the sporiferous leaves, one of these lobes is transformed into the ru- 

 diments of the sporocarps. This lobe is first divided into two equal 

 parts by a median cell wall, and each half then grows by an apical 

 cell to form the rudiments of the young sporocarp. At a very early 

 stage a ring-like wall is formed around the base of each rudiment, 

 and rapidly grows until it forms a cup, in which is contained the 

 papilla-likesporangial receptacle. This cup finally closes at the top 

 and thus forms the closed capsule in which the sporangia are borne. 

 In the smaller sporocarps a single macrosporangium, which almost 

 completely fills it, is formed, and this originates directly from the 

 apical cell of the sporocarp-rudiment. The microsporangia are pro- 

 duced many together, and the sporocarps containing them are larger. 

 The development of the two sorts of sporangia is at first much the 

 same, and follows closely that of the ordinary ferns, so much so, in- 

 deed, as to leave no doubt that Azolla is closely related to them. 



A comparison of the whole sporocarp with the sorus of certain 

 ferns shows that its wall is really homologous with the indusium of 

 the latter. 



If we examine the earlier stages of the macrosporangium we can- 

 not fail to be struck with its extraordinary resemblance to the young 

 ovule of many phanerogams, and the form and position of the indu- 

 sium suggest immediately its homology with the first integument of 

 the ovule. This is not so surprising when we remen.ber that the 

 ovule is really nothing but a specially modified sporangium. 



Up to a certain point the two kinds of sporangia develop alike, but 

 a difference becomes evident just before the formation of the spores. 



