197 

 A Critical Review of south Australian prasophylla 



TOGETHER WITH A DESCRIPTION OF SOME NEW 

 SPECIES. 



By R. S. Rogers, M.A., M.D. 



[Read June 1, 1909.] 



Plates VII. to XIII. 



The genus Prasophyllum is admittedly the most difficult 

 and perplexing one in the whole of the Orchidese. Not only 

 are the flowers frequently of very small size, but there are 

 so many intermediate forms that almost every species may 

 be said to blend insensibly into another. Even on the same 

 spike considerable variations are often to be found 

 among the individual flowers. A field observer who has paid 

 special attention to this group rarely has difficulty in assign- 

 ing any specimen to a particular species, but when it becomes 

 necessary to record those salient points which definitely serve 

 to distinguish one species from another his troubles begin. 

 Constant characters are not easy to find, and it becomes 

 necessary for differential purposes to depend upon the pre- 

 ponderance of certain characters rather than on their fixity. 



For the formation of his primary sections of this genus 

 Bentham relies upon the mode of attachment of the labellum 

 to the column, a character too fickle to form a good basis for 

 classification. Even cohesion of lateral sepals on which much 

 of his ultimate analysis depends can be regarded only in a 

 general way. In P. elaf/um, where this is perhaps a more 

 constant feature than in any other prasophyllum, I have 

 occasionally found the sepals free. Excessively dry and hot 

 weather is often responsible for this, and in some species 

 there is a tendency for separation to take place in adA^anced 

 maturity, though the sepals may be connate in the younger 

 flowers. In the contrary way I have sometimes found the 

 lateral sepals united in species where these segments are 

 usually free. 



The study of this genus cannot be conducted by means 

 of herbarium specimens alone, as even when such specimens 

 are softened in the usual way, the observer may be still very 

 much in doubt on many important points. Fresh specimens 

 and careful observations in the field are absolutely essential 

 to a right understanding. 



Flowers belonging to plants of the same species vary 

 a great deal in size according to the conditions under which 

 they grow, but the relative proportion between the petals 

 and lateral sepals seems (within narrow limits) to be fairly 



