88 VEGETABLE ORGANOGRAPHY. 



Dicotyledonous families which have constantly or usually 

 a single envelope to the flower. Jussieu, deciding the 

 question, has given them the name of ApetaLjE, and to 

 their envelope that of calyx ; on account of the un- 

 certainty which exists, I have decided to call these 

 plants Monochlamyde^e, and their envelope a Peri- 

 gone, neutral terms, which express a fact without 

 declaring an opinion. 



The reasons for which this envelope may be compared 

 to a calyx, are: — 1st, its extreme analogy with the 

 calyces of plants which are accidentally devoid of petals ; 

 2d, its frequent adhesion with the ovary ; 3d, the 

 greenish and foliaceous appearance of several ; 4th, the 

 analogy of structure of several monochlamydeous fa- 

 milies with those usually furnished with petals, such as 

 Amaranthaceae with Caryophylleae, Juglandeae with 

 Terebinthaceas, Euphorbiaceae with Rhamneaa, Elasag- 

 nese with Combretaceae, &c. ; 5th, the existence in 

 several, especially in Thymelaeas, of small petaloid scales, 

 which may be true petals. 



On the other hand, I consider that the external sur- 

 face of these single envelopes has all the characters of 

 a calyx : it is usually green ; it constantly presents 

 stomata, even when it is coloured, as in the Marvel of 

 Peru ; it frequently bears hairs or glands analogous to 

 those of the leaves, as in Elaeagnus ; but the inner 

 surface almost always presents the characters peculiar to 

 the sexual organs ; it is coloured, has no stomata, and 

 bears neither hairs nor glands analogous to those of the 

 leaves. We might conclude from these facts that it is 

 a calyx lined internally by the torus, or a petaloid ex- 

 pansion of it. This hypothesis would be confirmed by 

 this consideration, that with the exception of the Ama- 

 ranthaceae, which must, perhaps, be placed among 

 Thalamiflorae by the side of the Caryophyllea?, all the 



