182 ORGANOGRAPHY. BOOK I. 



ever, in Euphorbiaceae, in many of which Mirbel has 

 noticed tliat, after fertiHsation, the axis of the nucleus and the 

 endostome is inchned five or six degrees, without the exos- 

 tome changing its position ; by this circumstance the foramen 

 of the secundine and that of the primine cease to correspond, 

 and the radicle, instead of pointing when formed to the exos- 

 tome, is directed to a point a short distance on one side of it. 



Besides the two external integuments, Mirbel has re- 

 marked the occasional presence of three others peculiar to 

 the nucleus, which he calls the tercine, quartine, and quintine. 



The former is the external coat of the nucleus, and is very 

 generally, if not universally, present. As I am almost unac- 

 quainted either with it or the two latter, I can add nothing to 

 the following remarks of Mirbel upon the subject: — "The 

 quartine and quintine are productions slower to show them- 

 selves than the preceding. The qviartine is not very rare, 

 although no one has previously indicated it ; as to the quin- 

 tine, which is the vesicula amnios of Malpighi, the additional 

 memhrane of Brown, and the sac of the embryo of Adolphe 

 Brongniart, I am far from thinking that it only exists in a 

 small number of species, as Brown seems to suppose. If no 

 one has noticed the quartine, it is, no doubt, because it has 

 been confounded with the tercine ; nevertheless these two en- 

 velopes differ essentially in their origin and mode of growth. 

 I have only discovered the quartine in ovules of which the 

 tercine is incorporated at an early period with the secundine ; 

 and I think that it is only in such cases that it exists. At its 

 first appearance it forms a cellular plate, which lines all the 

 internal surface of the wall of the cavity of the ovule ; at a 

 later period it separates from the wall, and only adheres to 

 the summit of the cavity : at this period it is a sac, or rather 

 a perfectly close vesicle. Sometimes it rests finally in this 

 state, as in Statice ; in other cases it fills with cellular tissue, 

 and becomes a pulpy mass ; under this aspect it is seen in 

 Tulipa gesneriana. All this is the reverse of what takes place 

 in the tercine; for this thii'd envelope always begins by being 

 a mass of cellular tissue, (and at that time it has the name, as 

 we have seen, of nucleus,) and generally finishes by becoming 

 a vesicle. 





