784 



As to the manner in which these parasites acquire their destructive 

 power, Mr. Graham considers that it arises from the natural decay of 

 their mycelium or internal filaments, which he has found traversing 

 the tissues of plants, beneath the external tufts of mildew. That the 

 tissues of plants are extensively permeated by this mycelium, has been 

 frequently shown by the Rev. M. J. Berkeley and other mycologists ; 

 but the important fact that these roots (as they may be termed) die 

 within the tissues of plants, along with their superstructure, assuming 

 a dark colour in decay and ultimately dissolving into a viscous mass, 

 has hitherto, Mr. Graham states, escaped the notice of authors. De- 

 caying matter being thus secretly introduced, corrupts the adjacent 

 tissues, and in many cases spreads over the entire plant and kills it. 

 Mr. Graham states that he has arrived at this conclusion after re- 

 peated examinations under powerful microscopes, but that the effects 

 are visible in some cases to the naked eye. Experiments made by 

 enclosing tufts of mildew in the sap of those plants on which it grew, 

 also exhibited the results above stated. 



Double-flowered Variety of Matricaria CJtamomilla, by J. Hogg, 



F.R.S., F.L.S. 



Mr. Hogg exhibited dried specimens of a plant which he regarded 

 as a double variety of Matricaria Chamomilla, L., found by himself 

 on the sandy road-side near Whitburn, Durham, together with a co- 

 loured drawing of the natural size. He stated, in a communication 

 accompanying the exhibition, that he had never before observed any 

 similar variety of the species above named, nor could he find any ac- 

 count of its having been known to vary with a double flower. Sir J. 

 E. Smith, however, in his ' English Flora,' states of Anthemis nobilis, 

 that " varieties with double flowers are common in gardens ;" and in 

 Smith's own herbarium, in the Museum of the Society, are two spe- 

 cimens of Pyrethrum inodorum, \ar.Jlore pleno, the flowers of which 

 very strongly resemble those exhibited. These were found in Nor- 

 folk, by Mr. Crowe, in 1799, and are mentioned in the ' English Flora' 

 as " a double variety, having a multiplied radius and an obliterated 

 contracted disk." In the present example Mr. Hogg states that "the 

 external white petals, or rather the florets of the radius, are altogether 

 larger and stronger ; they are much elongated, strap-shaped, less nar- 

 row, with their margins somewhat folded inwards, and are rather more 

 numerous than those in the ordinary single flower, from which they 



