50 SELECTED NOTES FROM 



Aspidium. —The indusium in Aspidium ('Ao-ttic, a shield) is 

 peltate, attached by the centre ; in Nephrodium (Nttppoc, the 

 kidney), kidney-shaped, attached by the notch. H. F. Parsons. 



Young of Anodon cyg-neus.— These have, I beHeve, been 

 mistaken formerly for a parasite and described under the name of 

 Glochidium. The young shells show the black cross with polar- 

 ised light like those of the oyster-spat. This is due to the parti- 

 cles of carbonate of lime, forming the first layer of the young 

 shell, having their optic axes all in the same direction. When, as 

 in the older shell, layer upon layer has been deposited, the parti- 

 cles forming the thin section which we examine have their optic 

 axes pointing different ways, so that instead of the light which 

 passes through the axes of the two Nicol's prisms being totally 

 shut off, rays rotated by particles lying at a different angle come in 

 to take the place of those intercepted, and thus we have a more 

 or less general brightness instead of a dark cross. 



H. F. Parsons. 



Burweed (PI. VI., Figs, i — 4). — When travelling through the 

 wool-producing district of South Africa about two years ago, my 

 attention was directed by some gentlemen engaged in that import- 

 ant trade of the colony to a plant growing there called by the 

 above name ; at the same time, they explained the great trouble 

 caused by its seed-pods getting entangled with the wool, and 

 causing much damage to the machinery used in the process of 

 cleaning it. Hence, farmers and land-owners who allow the weed 

 to grow on their land are subject to heavy fines. 



I brought home a few of the seed-pods, which are as hard as 

 ebony, and contain two black seeds about the size and shape of 

 grains of wheat. The seed-pods are covered with exceedingly 

 hard, minute, hooked spines. These hooks are so formed as to 

 give the greatest amount of resistance to withdrawal. 



On comparing these hooks with those of the common burdock, 

 the latter are not so hard and of a weaker form compared with 

 those of the burweed. 



Plate VI. shows the seed entire and in section ; also the two 

 forms of hooks. H. N. Mavnard. 



Trichocolea tomentella (PI. VI., Figs. 6-9). — The cellular struc- 

 ture of this lowly plant shows it to be an apt illustration of the 

 law of association in the vegetable kingdom. Here we see the 

 cells compacted together to form the stem, and branching out to 

 form the leaves which foreshadow the leaves of the phaneroga- 

 mous plants. It is among the lower orders of plants — such as 



