234 Transactions of the Royal Microscopical Society. 
quoted a few cases of experiments, performed with Mimulus luteus, 
LIpomeea purpurea, Dianthus caryophyllus, and Petunia violacea, 
says :—‘‘ These few cases seem to me to possess much interest. We 
learn from them that new and slight shades of colour may be 
quickly and firmly fixed, independently of any selection, if the 
conditions are kept as nearly uniform as possible, and no inter- 
crossing be permitted. With Mimulus, not only a grotesque style 
of colouring, but a larger corolla and increased height of the whole 
plant were thus fixed; whereas with most plants which have been 
long cultivated for the flower garden, no character is more variable 
than that of colour, excepting perhaps that of height. From the 
consideration of these cases we may infer that the variability of 
cultivated plants in the above respects is due, firstly, to their being 
subjected to somewhat diversified conditions, and secondly, to their 
being often intercrossed, as would follow from the free access of 
insects.” “I,” says Mr. Darwin, ‘‘ do not see how this inference 
can be avoided, as when the above plants were cultivated for several 
generations, under closely similar conditions, and were intercrossed 
in each generation, the colour of their flowers tended in some 
degree to change, and to become uniform. When no intercrossing 
with other plants of the same stock was allowed, that is, when the 
flowers were fertilized with their own pollen in each generation, 
their colour in the later generations became as uniform as that of 
plants growing in a state of nature, accompanied at least m one 
instance by much uniformity in the height of the plants. But in 
saying that the diversified tints of the flowers on cultivated plants, 
treated in the ordinary manner, are due to differences in the soil, 
climate, &c., to which they are exposed, I do not wish to imply 
that such variations are caused by these agencies in any more 
direct manner than that in which the most diversified illnesses may 
be said to be caused by exposure to cold. In both cases the con- 
stitution of the being which is acted on is of preponderant im- 
portance.” 
In this last example, viz. Hypericene, I think you will see this 
verified ; the juice obtained from Hypericum is, as you know, of a 
reddish orange colour, turning red when treated with acid, but 
retaining its natural colour to a certain extent when prepared with 
oil. Our first spectrum, as shown in Fig. 11, represents this latter 
form. 
Fic. 11.—HYPERICENE IN OIL. 
| M. A. Observations. 
1 | D8. entros | 2.4 wa. 590° Class 1. Shaded; size °5. 
2 | 21°55 os ao) 60 554° Same as No. 1; size °5. 
3 | 19°00 | Commencement | 498- | General absorption. 
| 
