51 
and as the two conjugated lines of a ray s lie likewise on the com- 
plex cone of the focus P, they themselves are again rays s. 
The complex curve lying in a plane « we find by regarding the 
two poles A, and A, of «. The conjugated lines /,,/, of the lines / 
of @ pass respectively through A, and A,, and are conjugated by the 
rays / one by one to each other, so that two projective nets of rays 
are formed; the locus of the points of intersection of rays conjugated 
to each other is a twisted cubic through A, and A,, and furthermore 
through the four vertices of the cones 7,...7,; for, the two conju- 
gated lines of the line of intersection of « with 7,7,7', are AT, 
A,T. The rays s conjugated to the points P of that twisted cubic 
as foci lie in « and envelope the complex curve; and as each line 
of the plane 7',7,7', can be taken as a ray s conjugated toeg. 15, 
so also the line of intersection with «, the complex conic will touch 
the four surfaces of the tetrahedron. 
Botany. — “On the demonstration of carotinoids in plants” (First 
communication): Separation of carotinoids in crystalline form. 
By Prof. C. van WIssELINGH. (Communicated by Prof. Morr). 
(Communicated in the meeting of September 28, 1912). 
Many of the chemical, physical, and microscopical investigations 
on the yellow and red colouring matters of the vegetable kingdom 
which are grouped under the name carotins *) or carotinoids’) bear 
witness to great care and originality. They have, bowever, not all 
led to similar results. Especially the microscopical investigation has 
led to very divergent results which sometimes seriously conflict with 
those obtained by chemical and physical means. The investigators 
might be divided into two groups; one is inclined to consider all 
carotinoids identical; believing that the differences observed are not 
of a chemical nature. The other group distinguishes several carotinoids. 
T. Tammes ®) is especially a representative of the first group. After 
investigating a fairly large number of plants, she comes to the 
conclusion that the yellow to red colouring matter of plastids, in 
green, yellow variegated and etiolated leaves, in autumn leaves, in 
flowers, fruits and seeds, in diatoms, green, blue, brown and red 
1) Gzapex, Biochemie der Pflanzen, I. p. 172. 
2) M. Tswerr, Über den makro- und mikrochemischen Nachweis des Carolins, 
Ber. d. d. bot. Ges. 29. Jahrg., Heft 9, 1911, p. 630. 
3) T. Tamues, Uber die Verbreitung des Carotins im Pflanzenreiche, Flora, 
1900, 87. Bd. 2. Heft, p. 244. 
