Mr. Griffith on the Ambrosinia ciliata of Roxburgh. 27.3 



With regard to the earlier stages of development I may observe, that I was 

 aware some time before the date of these examinations of Mr. Robert Brown's 

 opinion as to the comparatively late origin of the integuments of most ovula, 

 and I consider the present instance as a good example of the correctness of 

 the views of this illustrious botanist. 



I have nothing to state regarding the reduction of one envelope, or the 

 limited extent of the tegument resulting from the original nucleus ; nor have 

 I yet positively determined the nature of the cellular membrane occupying 

 the fundus of its cavity. I am led however to think it to consist of the 

 remains of the sac of the amnios, which so frequently line the cavity of the 

 nucleus of other plants. 



The whole of the anomalies existing in the structure of the embryo may, I 

 think, be referred to the density of the texture of the nucleus and to the 

 shape of its cavity. 



The direction of the radicle is an instance of an exception to a very general, 

 and, within certain limits, perhaps universal rule. I allude to the corre- 

 spondence of the apex of the radicle to the same part of the nucleus, and 

 consequently to the situation of the original opening through the coat or 

 coats of the ovule. This exception however appears to me to be highly 

 corroborative of the validity of the law, since in the earlier periods of de- 

 velopment the direction is not only rectilinear, but the apex corresponds 

 exactly with the apex of the nucleus and with the foramen*. Another cir- 

 cumstance is likewise to be kept in view, viz. that the law just stated is 

 applicable only to the direction of radicles of embryos, which remain inclosed 

 in the original nucleus, or in some modification of its original form. The 

 perforation of the testa depends upon this anomalous direction of the radicle, 

 and somewhat perhaps on the compressed situation of the seeds themselves. 



The separation of the chief part of that portion, which is evidently from its 

 direction the cotyledon, is most remarkable, and forms another exception to 

 a general law. I allude to the very general absolute necessity of the coty- 

 ledons. I am however inclined to think from this and some other instances, 

 that the presence of a highly developed plumula occasionally obviates this 



* I would limit the expression of the above law to " radicle pointing or corresponding to the apex 

 of the nucleus ;" since there are exceptions to its correspondence with the foramen. 



