360 Mr. J. Miers oji the Extei'nal Coatings of Seeds. 



coat has emanated from the growth of the placentary expansion 

 that served as the support of the ovule, and that it has not been 

 developed from one of its proper tunics. Such is the coating I 

 call an arilline, in contradistinction to the testa, or development 

 of one of the proper tunics of the nucleus, which becomes an 

 integument always devoid of vessels, and generally crustaceous 

 in its texture, whence its name has been assigned ; but as this 

 is often reduced to the tenuity of a membrane, sometimes agglu- 

 tinated to the tegmen, and frequently to the arilline, as in the 

 Almond ; or as it sometimes happens that a still more extraneous 

 coating or arillus, formed over the arilline, or possibly the aril- 

 line itself, assumes the crustaceous form of the ordinary testa, 

 great misconception has existed in regard to the origin of such 

 integuments, and much confusion has ensued in the terms ap- 

 plied to them. It is true that the pouch or expansion of the 

 placentary sheath above described has often been confounded 

 with, or denominated, the primine ; but that does not influence 

 the real state of the case, for in this investigation we must de- 

 pend solely upon facts, that is to say, upon the nature of the 

 integuments themselves, rather than upon the designations which 

 botanists have often confusedly applied to these different deve- 

 lopments. It was therefore with the object of ascertaining the 

 real nature of the several kinds of seminal integuments, that I 

 entered into this investigation; and in now bringing it to a 

 close, I will subjoin the following elucidation of the real source 

 of the peculiar development which I have above described. 



The expansion of the placentary sheath and the peculiar 

 growth of the arilline offer well-marked 

 characters in many families, and these 

 developments take place under very 

 striking circumstances in the Anacar- 

 diacea. It has been assumed, as one 

 of its leading features, that its solitary 

 ovule is always suspended from a long 

 free thread that rises from the base 

 of the cell ; this, however, very rarely 

 happens, as I will show in a memoir 

 where the structure of the Order is 

 examined, and characters are given of 

 its various South American genera. I 

 now exhibit in the margin a drawing 

 (fig. 2) of what I have observed in 

 Pistacia Atlantica, that genus offering 

 one of the few cases where the funicle 

 rises from the very base of the cell : to 

 this is added a section of the same. Here the cord of nourish- 



FiK.2. 



