1 88 1 -8 2.] Edinburgh Naturalists' Field Club. 41 



the possession of two outer floral envelopes, the calyx and corolla, of 

 four or five parts each, marked generally by a difference in colour, the 

 calyx as a rule being green. These surround the essential organs 

 of the flower, the stamen and pistil or pistils, which are generally 

 correlated in number to the parts of the calyx and corolla. In 

 Monocotyledons, as a rule, there is no difference between calyx and 

 corolla — at least, as regards colour. There is one floral envelope 

 of six parts, in two alternating whorls, of which the three outer 

 may be taken to represent the calyx, while the three inner repre- 

 sent the corolla. The various parts of the flower represent a ter- 

 nary arrangement, quite distinct from the quinary or quaternary 

 arrangement of Dicotyledons. These two may be contrasted by 

 setting side by side their typical floral formulas, thus — 



Dicotyledons, . . 5 S. 5 P. 5 A. 5 G. 



Monocotyledons, . . 3 + 3 P. 3 + 3 A. 3 G. 



It is, however, in the character of the embryo that the essential 

 distinction in the reproductive organs lies. Within the coat of the 

 seed, such as the Pea or Bean, representing Dicotyledons, are two 

 hemispheroid masses placed face to face with each other. These 

 are the cotyledons or seed-leaves, the primary nutritive organs, 

 being in fact storehouses of nourishment for the young embryo. 

 Dicotyledons, as the name imjjlies, possess two of those seed-leaves, 

 while Monocotyledons possess only one. Acotyledons is a ques- 

 tionable term, inasmuch as it indicates a negative character. It 

 denotes the absence of cotyledons — reproduction, as already stated, 

 being effected by spores. In its higher forms it presents the pecu- 

 liar reproductive phenomenon of an " Alternation of Generations." 

 This is well seen in a Fern, from the spore of which a prothallium 

 is produced which leads an independent life. From this prothallium 

 the reproductive organs, antheridia and archegonia, are developed, 

 which, by a true process of fertilisation, in turn give rise to the 

 spore-bearing Fern. 



d. II. These three groups, founded on the primitive nutritive 

 organs in the seeds, represent the natural classification of Jussieu ; 

 and it is not a little interesting to trace the various steps by 

 which he arrived at such a classification, and its claim to the title 

 " Natural." The honour of distinctly defining what a true classi- 

 fication of the Vegetable Kingdom should be, is due to an English- 

 man, John Eay (1703). He maintained that a true classification of 

 the vegetable forms of life is one which exhibits a gradation from 

 the lower forms to the higher, and thus becomes the expression of 

 the plan observed in nature in the creation of living things. From 

 this, it would appear, arose the term " natural," contrasting with 

 other classifications which were termed " artificial." Ray, how- 



