362 ME F. O- BOWEB ON APOSPOEY IN PEENS. 



of flattened structures, consisting only of parenchymatous, chlo- 

 rophyll-containing cells, which, sooner or later, show at one or 

 more points on their margins that growth with a wedge-shaped 

 apical cell which is well known as characteristic of the Fern 

 prothallus ; root-hairs are at the same time formed by the out- 

 growth of individual cells (Plate XI. figs. 6, 7). None of my 

 cultures have as yet formed sexual organs : this we must wait 

 for ; but meanwhile it may be remarked that Mr. Druery's obser- 

 vations during the last two years show that, in the cases observed 

 by him, sexual organs were formed, and young Fern-plants were 

 produced by them. In any case, however, the above observa- 

 tions show that in the Fern in question there is a transition 

 from the sporophore generation to a structure of a prothalloid 

 nature, without the intervention of spores, and that it is formed 

 by a process of purely vegetative growth from more or less reduced 

 sporangia. Finally, it may be stated that my observations do 

 not exclude the possibility of a formation of such structures by a 

 vegetative outgrowth of the base of the sorus itself; whether 

 this actually occurs must be decided by further investigation *. 



Through Mr. Druery I have Mr. Gr. B. Wollaston's permission 

 to mention a still more interesting example of apospory, of which 

 the latter gentleman is the discoverer, viz. Polystichum annulare, 

 \ ar. pulcJierrimum. Here flattened organs, of undoubted prothal- 

 loid nature, are formed by simple vegetative outgrowth of the 

 tips of the pinnules, and without any connection with sori or spo- 

 rangia. At first the tip of the pinnule merely extends, so as to 

 form a flattened expansion, one layer of cells in thickness, and 

 with a very irregular margin ; while the whole tip curves down- 

 wards, and often forms a spiral coil of one, or one and a half turns, 

 closely covered above by the more expanded portion of the pin- 

 nule. In other cases the outgrowth may assume very irregular 

 forms. Ultimately the characteristic marginal growth begins at 

 some point, sometimes terminal, but more frequently lateral. The 

 details of this development have not yet been fully investigated. 

 The result, however, is the formation of a flattened, often heart- 

 shaped expansion, with a thickened cushion similar in structure 

 to that found in normal prothalli ; it bears antheridia and arche- 

 gonia of normal structure ; sometimes, as occurs also in ordinary 

 prothalli, they are found both on the lower and upper surfaces. 



* Since the above was written the cultures at Kew have progressed so that 

 prothalli bearing archegonia and antheridia may be seen, still connected at 

 their bases with the pinnule of the parent plant (PI. XII. fig. 8).— Feb 11, 1885. 



