Anatomie. — Biologie. 377 



metry is also to be observed more or less distinctly in the 

 cotyledons of the other five Monocotyledonous Orders examined. 

 This general occurrence of a twofold symmetry in the Mono- 

 cotyledonous cotyledon, which, moreover, is especially well 

 marked in the more primitive types ( Anemarrhena) suggests 

 the possibility of a fusion of seed-leaves in some remote an- 

 cestor to form the now single cotyledon. 



Further evidence in favour of this Suggestion is brought 

 forward in Part. II where the structure of a number of diii'e- 

 rent Dicotyledonous seedlings is considered. A list of about 30 

 different species in which the two cotyledons are partially 

 united by one or both margins is given, and also of about 10 

 other plants which possess a single cotyledon the true nature 

 of which is as yet uncertain. Several Ranunculaceous seedlings 

 in which the fusion of the cotyledons is especially well shown 

 are described in detail; and the conclusion is drawn from their 

 structure that the partial union between two cotyledons does 

 actually give rise to a reduced vascular System similar to that 

 existing in Anemarrhena. So closely do the two concrescent 

 cotyledons of Eranthis Mentalis resemble those of the coty- 

 ledon of Anemarrhena in their behaviour throughout that the 

 authoress believes that there is a common genetic connection 

 between them: that they are descended from a common ancestor 

 with two distinct seed-leaves, each represented by a single trace 

 in the hypocotyl. 



It follows from this view that the Dlcotyledons should be 

 regarded as a more ancient group than the Monocotyledons, 

 and in Part III the authoress proceeds to shew that this idea 

 is not at variance with the present state of botanical knowledge. 

 The paper concludes with the consideration of the principal 

 factors concerned in the origin of the Monocotyledonous habit. 

 In the course of the discussion it is pointed out that those 

 Dlcotyledons which posses fused cotyledons also exhibit ccrtain 

 other characters in common with the Monocotyledons which 

 seems to indicate that the habit of life that leads to the partial 

 union of the cotyledons in certain Dlcotyledons is essentially 

 similar to that of the Monocotyledons in which this union is 

 assumed to be complete. For instance, their hypocotyl is 

 nearly always much thickened and reduced in length. The 

 mature stem in a great majority is short, subterranean and 

 tuberous. In many the vascular bundles are isolated in the 

 tuber and secondary thickening is scanty or absent; and so on. 



D. J. Gwynne-Vaughan. 



Ursprung, Alfred, Der Oeffnungsmechanismus der 

 Ptertdophyten -Sporangien. (Jahrbücher für wissenschaft- 

 liche Botanik. Bd. XXXVIII. 1903. Heft 4. p. 635— 66b. 

 Mit 5 Textfiguren.) 



Eingehendere Studien lagen bis dahin nur vor über das 

 Polypodta'ceen-Sporang'mm, dem sich in neuester Zeit das 



