28 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



were sufficient to indicate that this is essentially different from the long: 

 secreting trichome of the other type. Fig-. 7, ff, shows a cross-section of a 

 head which has reached the 5 -celled stage. The fifth cell is formed by 

 the laying down of a radially placed wall by which the mother-cell is divided 

 unequally. In fig. 7, /, each of the 4 cells is divided by a radial wall, so 

 that the mature, or 8-celled, condition has resulted. 



Pio. 7.— Trichomes of Juglans nigra: a to e, long secreting trichomes (a, 6, e, d, and e X 535) ; 

 / to j, long secreting trichomes of the type having a head of more than 4 cells ( /, g, and h, 

 X535; iand jx 84); *: to «, short secreting trichomes, of which n tor are from thereglonofthe 

 veins of the leaves and s is from the leaf-margin (ft, I, and <>, X 1^0; m, /i,p, 5, r, «, and t, 

 X535). (Reduced one-flfth). 



In several trichomes the head was observed to be composed of 7 cells 

 only, but whether these were immature or not was not determined. From 

 a careful study of this type of trichome it would seem that 8 is the usual 

 number of cells in the head. No measurements were made on the length 

 of the heads, but the following numbers, in h-, give the diameter for the 

 type of trichome in question. The measurements were made only on 

 what were thought to be mature forms. Diameter of heads: 54.6, 50.4, 



