1 88 1 -82.] EdiiiburgJt Naturalists Field Club. 39 



Cereus niger, Cactacefu. \ 



Euphorbia sp., Euphorbiaceoe. \ 



( Columnar form. ) 



Mammillaria Dolichocentra, . . Cactaceoe. | 



Euphorbia melliformis, . . . EuphorbiaceEe. \ 

 (Glohular form.) 



X.—AGOTYLEDONS, MONOCOTYLEDONS, AND DICOTYLE- 

 DONS: THEIR MORPHOLOGY AND PHYSIOLOGY. 



By Mr WILLIAM LUNDIE. 

 {Read Feb. 23, 1882.) 



The two questions discussed were — 



(a) What are the distinctive characters by which these three groups 



are recognised ? 

 {h) On what grounds did Jussieu claim for this classification the 



title Natural f 

 Q. I. The distinctions are of two kinds, — morphological, i.e. such 

 as have reference only to form ; and physiological, i.e. siTch as have 

 reference to function. The morphological distinctions become quite 

 apparent when we contrast the Fern, the Lily or Palm, and the 

 Eose, as representatives of the three groups. The absence of what 

 would represent the aerial stem of the Eose, the peculiar form of 

 the frond, and the total want of anything resembling a flower, are 

 characters which strike us as peculiarly characteristic of a Fern. 

 Again, the branching of the stem in the Eose, its woody character, 

 the number of floral envelopes (two — calyx and corolla), the number 

 of parts (five) in each, and the character of the embryo, clearly 

 separate it from the Lily or Palm, which have an unbranched stem 

 (caudex), a single floral envelope of six parts (Lily), and a single 

 cotyledonary embryo ; while none of these characters are possessed 

 by the Fern. The physiological characters are equally marked, 

 and are connected with the functions of nutrition and reproduction. 

 The nutritive organs are those by which the life of the plant is 

 maintained, and consist, in the lower forms of vegetable existence, 

 of a thallus, and, in the higher forms, of root, stem, and leaf. The 

 reproductive organs, on the other hand, are those by which the 

 species is perpetuated, and consist of spores in the lower forms, and 

 of a flower and fruit in the higher. The greatest diversity in those 



