64 



occurs definitely in the Norfolk Broads, in Berks, and Gloucester. 

 Its continued distribution throughout the south-eastern counties 

 generally on suitable water may be fully expected. 



The Jumper's Pond Azolla was first noticed in the spring of 

 1914 by Mr. A. J. Rainer. He is confident that it was not there 

 in the previous year. Mr. J. Omer Cooper soon afterwards 

 brought me a specimen which I identified as Azolla. During the 

 summer of 191 4 it completely covered the pond. 



Pilularia glob ulif era, or Pillwort, from its pill-like " fruits," is 

 generally distributed throughout England and Scotland, but is 

 very rare in Ireland. It is fairly common and where found, luxuri- 1 

 antly so, in the New Forest on the muddy edges of streams and 

 " plashes " by the road sides. 



Azolla and Pilularia belong to a group of ferns which is 

 characterised by an aquatic or amphibious habit and by hetero- 

 spory. Otherwise they are widely different. In order the better to 

 understand the intricate life history of these two ferns it will be 

 wise to go over briefly the main features of the life history of an 

 ordinary fern. For fuller treatment both of this and the story of 

 Azolla and Pilularia, the student is recommended to read D. H. 

 Campbell's " Mosses and Ferns" (Macmillan and Co.) 



It will be known to all that on the back of the frond of a 

 common fern like the Male fern or the Hart's Tongue are well 

 defined areas where spores are formed. An examination with a 

 hand lens shows a large number of stalked spore-cases ; the 

 sporangia, grouped beneath a membranous covering, the indusium 

 and comprising the sorus. The spores are distributed by the wind 

 and, falling on suitable soil, germinate and give rise to green flat 

 heart-shaped structures, some one-third of an inch across at the 

 widest, the fern-scales or prothalli. The sporangia, the spores and 

 the prothalli are each all of one kind. The prothallus roots itself 

 and grows. On it develop two different sexual organs : the 

 archegonia, which contain the female egg, and the antheridia with 

 the male motile sperm-cells. After fertilisation the egg develops 

 into an ordinary fern plant as we know it, not into another fern- 

 scale, — that is produced only from a spore falling from the back of 

 a fern frond. There is thus a well marked Alternation of Genera- 

 tions : a fern plant, giving only spores, the sporophyte, and a 

 fern scale or prothallus yielding sexual cells or gametes, the 

 gametophyte. So much in brief for the ordinary Homosporous 

 Fern. With the Azolla and Pilularia the case is different and 

 much more obscure. Though there is superficially a resemblance 

 in plan of reproduction between these two genera, the one typical I 

 of the Salviniaceae and the other of the Marsiliaceae they are in I 

 reality widely removed from one another and show no true I 

 alliance. They must, therefore, be considered apart. 



The sporangia of Azolla are of two kinds, the micro-m 

 sporangia, with many small spores, the microspores, from which I 

 develop much reduced prothalli, upon which in turn are pro- i 

 duced the male organs or antheridia and within these the sperms I 



