1 88 1 -82.] Edinburgh Naturalists' Field Club. 43 



vegetative or nutritive organs, these must possess the highest 

 relative vahie, and will afford characters of a primary distinction. 

 Next in importance he placed the organs with which the plant 

 cannot dispense if its race is to be preserved — viz., those of repro- 

 duction, since nutrition is antecedent to and finds its ultimate end 

 in reproduction or the perpetuation of its species. In this way 

 Jussieu was led to adopt the primary nutritive organs — the 

 cotyledons — as the structures which present the highest relative 

 value, and whose structural differences, being of primary import- 

 ance, afford the first and best characters on which to base a classifi- 

 cation. Acotyledons, Monocotyledons, and Dicotyledons are thus 

 founded on those characters of the embryo which are of the widest 

 distinction, and yet exhibit a gradation from the lower forms to 

 the higher, conforming to the principle of a natural classification 

 enunciated by Eay, The simplest and lowest types of structure 

 in the vegetative organs is to be seen among the Cryptogams or 

 Acotyledons, where, in many cases, a single cell carries on both 

 the functions of nutrition and reproduction ; while, a stage higher, 

 we have cells combined to form a tissue — the Thallus. The 

 highest differentiation of cells, and the most complex nutritive 

 process in the embryo, is observed among Dicotyledons ; while in 

 Monocotyledons it represents an intermediate stage. 



In illustration of the above paper, the following preparations 

 were shown under the microscope — viz. : 



1. Transverse section of Acer of the first, second, and third year's 



growth, and one or two abnormal forms, — all representing 

 Dicotyledons. 



2. Transverse section of Sugar-Cane, Euscus, and Dracfena, 



representing Monocotyledons. 



3. Transverse section of Pteris (Fern) ; apical longitudinal sec- 



tion of Chara, showing growth ; Prothallium of a Fern 

 with antheridia and archegonia, — all representing Acoty- 

 ledons. 

 Besides these, there were hand-specimens to show their morpho- 

 logical characters. 



