492 SUMMARY OF CURUENT RESKARCIIES RELATING TO 



the ordinary character developed iu the axils and on the superior 

 surface of the jjinnie, and agreeing iu character with the ordinary 

 bulbils of Asplenium ; (2) bulbils formed apparently by transmuted 

 si)oro-producing energy, and occujjyiug the place of sori, i. e. on the 

 under side of the piuuas ; (3) j^roliferous prothalli arising i'roiu pseudo- 

 bulbils produced by a different transmutation of the reproductive 

 force, and evolving plants only after the })rothalli have pri)duced the 

 usual sexual organs common to prothalli resulting from spores. 



Prof. F. 0. Bower describes more minutely the details of this sin- 

 gular process iu Atlujrmm Filix-foimina var. clarissiina. Some of the 

 sporangia iu the transmitted sori are of nearly normal structure, with 

 an aunulus, and arrested only at a point of development before the 

 formation of the spores; the majority showed more or less the central 

 archcspore, together with the cells which would normally form the 

 wall of the sporangium ; but there the normal development is sud- 

 denly arrested ; the archespore has not divided further to form either 

 the tapetum or the mother-cells of the spores. The individual cells 

 are of larger size than ordinary, and contaiu numerous chlorophyll- 

 grains. Placed under favourable couditious, sporaugia of the latter 

 descriptiou undergo further development, producing, by a purely 

 vegetative process, outgrowths of very irregular form. Sometimes all 

 the superficial cells of the club-shaped si)oraugium may take part iu 

 the process ; sometimes the head is thrown oft', while the stalk, which 

 has previously attained an abnormally large size, continues its vege- 

 tative growth. The result iu either case is the formation of an 

 ordinary prothallium with wedge-shaped ajiical cell and root-hairs. 



Another instance of apospory is yielded by Puhjstichum angulare 

 var. pidcherrinmm. Here the arrest of development of the sporophore 

 is still more complete, organs of a prothalloid nature being formed by 

 simple vegetative outgrowth of the tii)S of the piuuules, without any 

 couuection with sori or sporangia. In the formation of these pro- 

 thalloid structures which bear normal autheridia and archegonia, the 

 tip of the pinnule usually forms a flattened expansion, only a single 

 cell in thickness, which ultimately developes, by marginal growth, 

 into a flattened, often heart-shaped, structure, with a thickened cushion 

 similar to that of normal prothalli. 



Anatomy of the Vegetative Organs of Struthiopteris germanica 

 and Pteris aquilina.* — M. P. Tcrletzki finds the rhizome of 

 Struthlojjteris (jermanica to exhibit exceedingly good illustrations of 

 continuity of protoplasm, both in the j^arenehyma and iu the sieve- 

 cells, the protoplasmic threads passing through both the longitudinal 

 and the transverse walls, especially the latter. The intercellular spaces 

 contain protoi)lasm which is also iu the same way in connection with 

 the cell-protoplasm. The arraugcmeut of the vascular bundles is 

 stated by the author to be here, as in almost all other Polypodiaccae, 

 bicollateral, and not concentric, as stated by De Bary and Sachs. By 

 far the most common form of thickening is the scalariform, accom- 

 panied in some cases by spiral and annular ;^ it produces, however, 



* riiiigsbcim's JaUih. f. Wiss. Bot., xv. (1881) pp. 152 501 (."5 pis.). 



