NOVEMBER 17, 1898. ] 
5.1145 Protoplasmic movements, irri- 
tability. 
5.11451 Heliotropism, 
hydrotropism, ete. 
See also growth. 
5.1146 Germination. 
See also 4.11151, 4.12, and 5.1143. 
5.12 Reproductive processes. 
5.121 Vegetative propagation. 
geotropism, 
Subdivided, when desired, either on morphological 
lines or by plant groups. Morphology, Organography 
and Ecology would be frequently consulted here. 
5.122 Sexual reproduction. 
5.1221 Differentiation of sex. 
5.1222 Heterospory, alternation of gen- 
erations. 
5.1223 Fecundation. 
5.1224 Reproduction of Thallophytes 
5.12241 Conjugation. 
5.12242 Oophytic fertilization. 
5.12243 Carpophytic fertilization. 
5.1225 Reproduction of Archegoniatee. 
5.12251 Bryophytes and Pterido- 
phytes. 
5.122511 Antherozoids. 
5.122512 Egg cells. 
5.12252 Gymnosperms. 
Subdivided like preceding. 
5.1226 Reproduction of Siphonogame. 
5.12261 Pollen and pollen plants. 
5.12262 Ovules. 
General morphology, 
tion, to be consulted. 
5.2 Ecology. 
5.21 Vegetative interrelations. 
5.211 Phenology. 
5.212 Nutritive adaptations. 
Embryology, and Germina- 
5.2121 Plankton, aquatics, ice plants, 
dew plants, etc. 
5.2122 Climbing plants. 
5.2123 Carnivorous plants. 
5.2124 Parasites, symbionts. 
5.213 Protective adaptations. 
5.2131 Compass plants, 
halophytes, xerophytes, 
plants, ete. 
Chloroplast movements and the protective adjust- 
ment of stomata would be sought under Physiology 
proper. This may be subdivided as needed. 
5.2132 Spines, secretions, raphides. 
See also 4.11, 4.222, and 5.1132. 
epiphytes, 
sleep of 
SCIENCE. (Aa 
5.21383. Myrmecophilism, acarophilism. 
5.22 Reproductive interrelations. 
5.221 Pollination. 
5,222 Dissemination. 
6. Vegetable pathology including the injuries 
of plants, and therapy. 
7. Evolution, natural selection, etc. 
8. Man’s influence on plants, artificial selec- 
tion, ete. 
Economic botany would be consulted here. 
9. Phytogeography, floras, ete. 
9.1 Geographical botany. 
Ecological considerations would be sought under 
Physiology. 
9.2 Floras. 
Subdivided, according to abundance in each area, 
geographically like periodicals, ete. Travelers’ jour- 
nals of restricted scope, and similar works directly or 
indirectly throwing light on a local flora, reports of geo- 
logical surveys, and even local maps and guide books, 
in a botanical library are brought together here for 
convenience in use. Fossil floras excluded from taxo- 
nomy would find place here. 
WILLIAM TRELEASE. 
MIssouRI BOTANICAL GARDEN. 
0.4 
ON THE CAUSE OF DARK LIGHTNING AND 
THE CLAYDEN EFFECT. 
I HAVE been criticized in a letter which 
appeared recently in Nature for not alluding 
in my letter on dark lightning to the pecu- 
liar photographic reversal known as the 
Clayden effect. I must confess that at the 
time of writing my letter I was unaware of 
this effect, a description of which has only 
appeared, so for as I know, in one of the 
photographic journals. Mr. Clayden has 
certainly explained dark lightning, and it 
only remains to explain his explanation. 
As I think that this effect is not generally 
known, I believe that it may be worth while 
to devote a few words to the statement of 
the case, before describing the experimen- 
tal work by which I have determined the 
factors which play a part in this very curi- 
ous photographic phenomena. 
Mr. Clayden showed that if a plate, which 
had received an impression of a lightning 
flash or electric spark, was subsequently 
