636 Vehicles of the Hereditary Characters. 
The second part of DARWIN'S Pangenesis is met by 
insuperable difficulties, and has long since been regarded 
as superfluous. DARWIN himself admitted that it had 
only a very limited application to plants and corals, to 
Fig. 144. Ulmus campestris varie- 
gatus. The variegated regions 
are developed in widely differ- 
ent extents on the different 
leaves. 
Fig. 145. Beta vulgaris saccha- 
rifera. A chance variegated 
leaf. The yellow and green 
tissues are superimposed upon 
one another in such a way 
that the limits of the indi- 
vidual layers do not corre- 
spond. 
investigations of BONNIER and FLOT. See G. BONNIER, Formation 
des elements dn cilindre central, Comptes rendus, Vol. CXXXT, p. 
781 (Nov. 12, 1900), and Sur la differentiation des tissus vascu- 
laires, loc. cit., p. 1276 (Dec. 1900); and LEON FLOT, Sur I'origine 
commune des tissus dans la feuille et dans la lige, loc. cit. (Dec. 1900). 
