HA RD WICKE'S S CIENCE- G OSS IP. 



exactly like those used for adjusting a theodolite. 

 The razor blade can be made by any blacksmith 

 accustomed to fine work, and must be made of the 

 best steel ; each end is clamped to the frame by a strip 

 of brass, and two screws subsidised by indiarubber. 

 The way to use it : fill the tub with ice ; sprinkle on 

 salt ; screw on the lid ; put on the tissue on the 

 grating which will be hard in five minutes ; adjust 



Fig. 43. — Freezing Microtome. Plan of top. 



B 



-HE. 



A 



PLATE GLASS TOP 



JL^Z ! 



•RAZOR BLADE 



1 r 



Fig. 44. — Section of Freezing Microtome. 



the microtome by means of the three screws, A, B & C, 

 until the razor blade touches the tissue plane a slice 

 off, then lower the point by giving A half a turn, 

 plane off another section and so on. I have heard it 

 recommended to tip the screws, A, B & C, with ivory, 

 so that they would slide better on the plate-glass 

 cover, but I found the brass ones work beautifully. 

 Plymouth. B. Sc. 



THE ORIGIN OF DOUBLE FLOWERS. 



AFTER reading the papers on double flowers in 

 Science-Gossip recently, I felt encouraged 

 to talk about them to my neighbours, one of whom 

 showed me a bed of double stocks raised from the 

 seed of a solitary plant with single flowers, which, 

 growing in an isolated spot, had probably received no 

 pollen from the flowers of other plants. Here and 

 there a plant with single flowers might be found 

 among the lot I saw, but, besides being comparatively 

 few, the plants bearing single flowers were small and 

 weakly. The next gardener that I saw showed me 

 two zonal pelargoniums with double flowers. He said 

 that he had raised those plants from seeds, the 

 produce of a single flower, with which he had not 

 interfered, nor did he think that any insect had 



cross-fertilised it. He had found three ripe seeds 

 and sowed them. They all germinated, but one 

 seedling plant had died. The other two grew to 

 maturity, and each of them bore double flowers. 

 Thus we see how double flowers appear on plants 

 under cultivation without conscious effort on the 

 part of the happy gardeners who raise them. When 

 a plant appears which pleases its owner more than 

 others he takes the seed from that particular plant 

 and sows them apart from other seeds. If the plants 

 raised from such seeds are grown together, so that 

 their flowers inter-cross, the effect of such inter-crossing 

 is not like that of crossing freely with other plants 

 not so nearly related, but tends to fix any character 

 by which a variety may be distinguished from the 

 species. Florists often keep apart the seeds of such 

 a plant as they like best, having first been careful 

 that its flowers should not be crossed. So, without 

 •knowing or intending it, they make arrangements for 

 the appearance of double flowers. A striking 

 difference appears however between the solitary plant 

 with double flowers occurring among a lot of seedling 

 sweet williams and the two plants of zonal pelargonium, 

 each having double flowers, with no single flowered 

 seedling by their side. If the theory of Mr. Mott be 

 right, it would not be likely that so many double 

 flowers would appear among the offspring of a 

 young plant like Mr. Sim's sweetwilliam as among 

 those of an older plant under similar conditions. 

 Now it is well known that zonal pelargoniums 

 are extensively propagated by cuttings which 

 retain the character of the individual plant from 

 which they are taken, and survive for many years 

 to be like Moses in his old age, when the natural 

 force of his strength was not abated. If the flower 

 of such a plant be fertilised by its own pollen, or 

 by that of another flower on the same plant, or on 

 any plant derived from a cutting of the same stock, 

 nothing would be more likely than that plants grown 

 from seed so generated would bear double flowers, as 

 it seems they do. If Mr. Sim's sweet william be 

 kept for so long as it may live in a state of isolation, 

 so that its flowers be not crossed with strange pollen, 

 it would be interesting to know whether the plants 

 raised from its seed would bear an increasing number 

 of double flowers as the plant grows old. 



John Gibbs. 



Curious conduct of Pigeon.' — My attention 

 was called to a rather novel bit of Natural History 

 on Monday 6th January. It was in the conduct of a 

 pigeon playing and splashing on the water, enjoying 

 itself as if it was in its natural element. The same 

 thing occurred on Tuesday and Wednesday. When 

 it was startled it rose with perfect ease and flew back 

 to its loft. I can testify to its having been the same 

 pigeon on all three occasions. Can any readers assign 

 a reason for this occurring ? — A. W. Fry. 



