STRUCTURE.] CARUNCUL^ MICROPYLE CHALAZA. 31 



it is so large as to occupy fully a third part of the whole 

 surface of the seed, as in the Horsechesnut, Sapotads, and 

 others. Seeds of this kind have been called nauca, by Gart- 

 ner. In grasses, the hilum is indicated by a brownish spot 

 situated on the face of the seed, and is called by Richard 

 spilus. The centre of the hilum, through which the nourish- 

 ing vessels pass, is called by Turpin the omphalodium. Some- 

 times the testa is enlarged in the form of irregular lumps or 

 protuberances about the umbilicus; these are called strophioloB 

 or caruncula ; and the umbilicus, round which they are 

 situated, is said to be strophiolate or carunculate. Mirbel has 

 ascertained that in Euphorbia Lathyris the strophiole is the 

 fungous foramen of the primine ; and it is probable that such 

 is often the origin of this tubercle : but at present we know 

 little upon the subject. 



The foramen in the ripe seed constitutes what is called the 

 micropyle : it is always opposite the radicle of the embryo ; 

 the position of which is, therefore, to be determined without 

 dissection of the seed, by an inspection of the micropyle, 

 often a practical convenience. 



In some seeds, as the Asparagus, Commelina, and others 

 (fg. 188.), there is a small callosity at a short distance from 

 the hilum : this callosity gives way like a lid at the time of 

 germination, emitting the radicle, and has been named by 

 Gartner the embryotega. 



At the apex of the seed, in the Orange and many other 

 plants, may be perceived upon the testa a small brown, spot, 

 formed by the union of certain vessels proceeding from the 

 hilum : this spot is the chalaza (Plate VI. fig. 11. b}. In the 

 orange it is beautifully composed of dense bundles of spiral 

 vessels and spiral ducts, without woody fibre. The vessels 

 which connect the chalaza with the hilum constitute a parti- 

 cular line of communication, called the raphe : in most plants 

 this consists of a single line passing up the face of the seed ; 

 but in many Citronworts (Aurantiacese) and Guttifers it 

 ramifies upon the surface of the testa. 



