2l6 THE SCOTTISH BOTANICAL REVIEW 



On those fixed dunes, from which Pteris is absent, Ammophila is 

 almost a dominant type, and the association is a closed one. Many 

 of the included plants are those of cultivated land. In addition to 

 some of the species already mentioned as occurring in the bracken 

 association, the following are abundantly represented : — 



Geranium molle^ Linn. Leontodon 7mdicaiile^ B. & S. 



Galium saxafile, Linn. Rutfiex Acetosella, Linn. 



Bellis perefinis, Linn. Urtica dioica, Linn. 



Ctiicus lanceolatus, AVilld. Luzula campestris, D. C. 

 Cniciis arvensis, Hoffm. 



On the innermost margin of these fixed dunes Uiex europcsus is 

 occasionally met with. Mosses and lichens are common here, and 

 in the transitional associations. They play an important part in 

 preparing the ground for the growth of flowering plants. Here and 

 there on these fixed dunes limited areas have been enclosed and 

 are now under cultivation. It is impossible at this preliminary 

 stage in the study of the vegetation of this formation to form any 

 opinions on its composition and distribution which will be of 

 lasting value. The particular area which forms the subject of this 

 communication is too restricted in extent, in any case, for generalised 

 deductions. The mere listing of species included in the different 

 associations is but the initial stage in any ecological study. Were 

 these lists complete, much would yet remain to be done. Critical 

 forms must be made the subjects of careful investigation. A 

 thorough investigation of the dependent species and their habit of 

 life must be undertaken, to determine the relationship existing 

 between them and the dominant type, in the association in which 

 they occur. 



The powers of adaptation and adjustment to environment of the 

 individual plants, and many other kindred problems, still await 

 solution. 



The Past History of Monocotyledons, with Remarks 

 on their Origin. By A. R. Horwood. 



(With Two Plates. ) 

 ( Co)itinued frotn p. 1 80. ) 



4. Theories as to the Origin of Monocotyledons. 



There have been many theories as to the origin of monocotyledons. 

 They may be regarded as (i.) systematic, (ii.) morphological and 

 embryological in character. 



According to the former evidence monocotyledons are generally 



