37'4 Linnaa?i Society. 



the raphe within it. Sixth, we have thus the evidence complete of 

 the existence of the usual and distinct envelopes around the nucleus 

 of the seed, viz. an inner integument with its apical chalaza, an in- 

 termediate hard testa with its corresponding diapyle, through which 

 tlie nourishing vessels of the more exterior raphe penetrate, and the 

 whole included within a scarlet-coloured arillus. 



From all these facts it may be inferred, that the envelope, which 

 unquestionably is an arillus in the Garcinieee and Tovomit€(B, must 

 be of the same nature in the ClusiecB, and that which is arillus in 

 the Clusiece must be the same development in the MagnoUacecc ; that 

 which is granted in the one, cannot, Mr. Miers thinks, be denied in 

 the other. Although it be true tliat the several envelopes of the 

 seeds in different families are not to be recognized alone by their 

 consistency, which may be more or less membranaceous, ligneous, 

 cellular, or composed of oily or resinous granules according to cir- 

 cumstances, yet they may alwajj's be determined by their relative 

 position in regard to raphe, chalaza, diapyle, micropyle, hilum, &c. 



Connected with this question is that of the origin and mode of 

 growth of the arillus in seeds, which by St. Hilaire is described to be 

 of two kinds, the true and the false arillus, the former open at its 

 extremity, the latter entirely covering the seed. This view was 

 afterwards modified by Dr. Planchon, who gave to the false arillus 

 the name of arillode. Both kinds are alike in texture, form, and 

 colour, their difference consisting in this : — the arillus, whether ab- 

 breviated or entire, always covers the micropyle of the testa, while 

 the arillode constantly exhibits a minute or larger opening in its 

 surface around the micropyle, which is never covered by it. He 

 traces this distinction to their different sources of origin, attributing 

 the growth of the true arillus over the ovule to a gradual enlarge- 

 ment of the funiculus, noticing its first appearance from a mere 

 swelling of the umbilical cord to its gradual increment and ultimate 

 develoj)ment ; but the arillode, he states, is derived from an enlarge- 

 ment of the mouth of the exostome or foramen of the ovule, its 

 margins being reflected and produced over the primine, thus growing 

 upon it in the form of an additional tunic. In either case, it is, 

 therefore, clear, whether this accessory coating be arillus or arillode, 

 that the raphe, when it is free^ must necessarily be enclosed withn it. 

 In Euphorhiacea: this coating is considered by many botanists. Dr. 

 Planchon among the number, as merely an epidermis of the testa ; 

 but it becomes difficult to discriminate between a very thin arillus and 

 a thick epidermis, as both appear to be of the same nature, varying in 

 degree of thickness from one extreme to the other in different genera of 

 that family. The most instructive and conclusive evidence of the origin 

 and subsequent extraneous growth of the arillus over the ovule, has 

 been adduced by Cambess^des, who found in Casearia many incom- 

 plete seeds where the anatropal ovule remained in a state of com- 

 plete abortion, while the arillus had grown over it to its full extent, 

 proving that where the ovule had ceased to grow, the increment of 

 the funiculus was not stopped in its progress of extraneous develop- 

 liient.' ' According to the hypothesis of Dr. Planchon, the outer 



