Botanical Society of Edinburgh. 27t 



the spontaneous separation of the enclosed portion of the cotyledon, 

 the testa is frequently found ruptured, but Mr. Griffith does not con- 

 cur with Roxburgh in regarding this as the stage of germination, 

 which he thinks cannot be said to take place until the radicle has 

 elongated and the innermost of the plumulary processes become ex- 

 panded. The axis contains the rudiments of additional radicles, 

 which after germination become exserted. 



Mr. Griffith thinks that the whole of the anomalies existing in the 

 structure of the embryo may be referred to the density of the tex- 

 ture of the nucleus and to the shape of its cavity. The direction of 

 the radicle appears at first sight to be an exception to a very general 

 rule ; but this anomaly is proved to take place subsequently to the 

 earlier stages of development, during which the apex of the radicle 

 corresponds exactly with the apex of the nucleus and with the fora- 

 men. He adds in a note that he would limit the expression of the law 

 to " radicle pointing or corresponding to the apex of the nucleus," 

 since there are exceptions to its correspondence with the foramen. 



The perforation of the testa by the radicle is explained by the 

 anomalous direction of the radicle in the later period of its deve- 

 lopment ; and the separation of the chief part of the cotyledon by 

 the constriction exercised upon it by the indurated apex of the nu- 

 cleus. Mr. Griffith is inclined to believe from this and some other 

 instances that there is no absolute necessity for a cotyledon, but that 

 its presence may be supplied by a highly developed plumula ; the 

 enormous development of the plumula in the present case being evi- 

 dently adapted to correct what would otherwise be a destructive 

 anomaly. 



Finally, the author adduces the examination of this plant as a 

 striking proof of the advantages to be derived from tracing anoma- 

 lous forms back to the earliest period of their development. Going 

 back to the period immediately before the conical apex of the radicle 

 projects through that of the nucleus, we arrive at a stage when the 

 form of the embryo closely resembles the usual form of the Aroidece, 

 since we have a superior radicle, a cotyledon, and a tendency to the 

 formation of a lateral slit, as indicated by the depressed areola. 



BOTANICAL SOCIETY OF EDINBURGH. 



Feb. 12, 1846.— Dr. Balfour, President, in the Chair. 



A large collection of plants from Chippawa, Niagara, and various 

 parts of Canada, was presented from Dr. Philip W. Maclagan ; and 

 specimens of some of the rarer alpine plants of Scotland by Dr. Bal- 

 four. 



The following communications were read : — 



1. " On the Potato Disease," by John Goodsir, F.R.S.E., Demon- 

 strator of Anatomy in the University of Edinburgh, and Secretary of 

 the Botanical Society. 



In reference to the nature of the potato disease, Mr. Goodsir stated 

 that there could be no doubt as to its general resemblance to an epi- 



