NOTES ON RECENT RESEARCH. 



1119 



exotheciuru of the sac is detached along all its circumference, the walls 

 of the verticil of sacs of an anther rolling back as they shrink, like the 

 segments of a closing umbrella. Gingko differs from all other Conifers 

 and Cycads, and resembles Angiosperms in possessing a sub-epidermal 

 " endothecium " of hygroscopic reticulate cells in its anther-wall. The 

 twin pollen-sacs are parallel at first, and open by facing slits on the inner 

 side of each. As each sac dries it shrinks from the other and passes 

 through a right angle, so that the gaping slits now face directly down- 

 wards. — M. H. 



POLYCOTYLEDONY. 



Polyeotyledony, Morphological Note on. By Sir W. T. 



Thiselton-Dyer, K.C.M.G., C.I.E., F.K.S., Director Royal Gardens, Kew 

 [Ann, Bot. vol. xvi., No. 63, p. 553, with plates xxiv. and xxv., and figure 

 in text). — This is one of a vauable series of notes (No. viii.) contributed 

 from the unrivalled resources at Kew. The author writes : "It is the 

 object of these notes as much to suggest problems as to solve them. In 

 the present case, I propose to tell a story of which I do not quite see to 

 the bottom. . . . My friend, Professor Bayley Balfour, in a very sugges- 

 tive address which he delivered from the chair of Section K at the 

 Glasgow meeting of the British Association, gave a theory of the 

 Dicotyledonous Embryo, the main points of which I will emote : ' We 

 ought, I think, to look upon the embryo as a protocorm of embryonic 

 tissue adapted to a seed life. . . . Confining ourselves to the general 

 case, the axial portion of the protocorm of the Dicotyledon, the hypocotyl, 

 bears a pair of lateral outgrowths, the cotyledons, and terminates in the 

 plumular bud and in the primary root respectively. The cotyledons are 

 its suctorial organs, and the hypocotyl does the work of rupturing the 

 seed, and placing the plumular bud and root by a rapid elongation which 

 commonly brings the plumular bud above ground, protected, it may be, 

 by the cotyledons. These latter may then become the first assimilating 

 organs, unlike or like to the epicotylar leaves.' This, though a guarded 

 statement, appears to imply that the cotyledons are more or less organs 

 sui generis, and not homologous with ordinary or epicotylar leaves. It 

 brought to my recollection some observations which I made some years 

 ago, and which it now seems worth while to put on record. It is well 

 known that the Sycamore [Acer Pseudo-Platanus) reproduces itself spon- 

 taneously from seed with great readiness. ... A notable portion of the 

 seedlings of this tree (at Kew) came up with three cotyledons. The 

 circumstance is not, however, unusual, and similar cases are discussed 

 in Duchartre's classical ' Memoire sur les Embryons qui ont ete decrits 

 comme Polycotyle ' in the Annales des Sciences Naturelles (3 e ser., x., 

 pp. 210-211)." Duchartre is quoted at some length, but let us take only 

 his opinion. " 1 Je me borne h figurer ici deux de ces germinations, 

 choisies entre beaucoup d'autres ; dont l'une presente un cotyledon bifide, 

 tandis que l'autre en montre un profondement biparti. ... Si Ton 

 observe que la fente qui les separe descend un peu moins profondement 

 que celle qui existe entre les deux vrais cotyledons ; si, de plus, on fait 

 attention a la situation des deux petites feuilles primordiales deja 

 developpees, qui alternent avec le cotyledon biparti comme avec celui qui 



