1906.] Plants on a Photographic Plate in the Dark. 389 



is obtained from the paper. Fig. 6, Plate 20, is one obtained from the paper 

 on which an Auricula Hower has been squeezed, and fig. 7 is from an Oriental 

 poppy. Fig. 8 is from the petal of a viola. The colour of the petal does not 

 affect the result. Wbite, blue, and pink petals of the Canterbury bell, red and 

 white rose petals, dark purple and yellow viola petals and many others all 

 give similar results, and all, as far as rough experiment goes, appear to be 

 active to about the same extent. They show, however, greater activity than 

 an equal area of the leaf of the same plant. 



The pistil in a number of plants, for instance, poppy, lily' cactus, tulip, 

 iris, etc., were examined, and in all cases were found to be very active. The 

 stamens of different plants when squeezed were found to be active, but 

 pollen, on the contrary, when examined alone was always found to be quite 

 inactive. That from the sedge, hazel, Scotch fir, Pinns pinaster, Pinus cembra, 

 and many other plants was examined. 



Leaves. — Carrying the investigation on to leaves, large numbers have been 

 experimented with, and all have been found to act on a photographic plate. 

 The amount of action naturally varies with leaves from different plants ; 

 where there is much sap juice, there is generally much action. If a leaf be 

 simply dried its activity is much lessened, or may be nearly destroyed, and 

 its surface is rendered uneven ; but even in old and dried leaves a very 

 appreciable amount of activity remains. For instance, beech leaves picked 

 up off the ground were found to have about the same degree of activity as 

 the ordinary green leaf, and a canna leaf which had been between blotting 

 paper in a press for one and a-half years, and other leaves which had been 

 pressed for two to three years, still were able to give a faint picture. If these 

 old leaves were slightly moistened before putting up with a photographic 

 plate, this activity was considerably increased (figs. 9 and 10). Also it is 

 interesting to note that if a slit be cut in the dry leaf, this becomes in 

 the picture very visible. Fig. 11 appears as if an active emanation had taken 

 place from the body of the leaf. The best way of obtaining satisfactory 

 pictures of leaves is to subject them to considerable pressure between white 

 (Ford) blotting paper ; this, of course, squeezes the leaf juice out and the 

 leaf is left in such a condition that after standing in the air for a short time 

 it may be put up with the photographic plate. Whether the squeezing 

 should be repeated, and whether the pressure should be a quarter of a ton or 

 six tons, depends on the nature of the leaf experimented with. This way of 

 drying a leaf has also the advantage, as previously pointed out, of giving a 

 second picture, which is often a very interesting one, and is simply obtained 

 by exposing the paper with the absorbed sap from the leaf to a photographic 

 plate. 



