PURE SPECIES AND HYBRIDS OF JUGLANS. 23 



trichomes from analogous situations only are compared, so that the results 

 in such cases may be considered just. Following- are measurements, in p, 

 on the length and diameter of the heads of the long- secreting trichomes 

 which were taken from the veins of the leaves: length, 29.4, 31.5, 35.7, 

 33.6, 33.5, 31.5, 29.4, 25.2, 29.4, 29.4, 33.6, 25.2; diameter, 25.2, 23.1, 

 29.4, 25.2, 25.2, 27.3, 29.4, 31.5, 25.2, 25.2, 29.4, 27.3. The diameters of 

 the heads are the diameters seriatim of those whose lengths are given pre- 

 viously. The heads average 30.6 p- in length and 26. 8 /A in diameter. In 

 length the variation from the average is 13 per cent, and the variation 

 from the average diameter is 15 per cent. 



The material of Juglans calif ornica which was put up was not favorable 

 for the study of the youngest stages in the development of the short secreting 

 trichomes, so that a description of the mature organ only is possible in this 

 place. The trichome is made up of 6 cells, of which 2 constitute the stalk 

 and 4 the head (fig. 5, i to 0), which are so placed as to form a disk 1 cell 

 in thickness. 



A character which easily distinguishes the short secreting trichomes of 

 Juglans calif ornica from those of Juglans regia or Juglans nigra is the length 

 of the head-cells. As the figures indicate, the cells of the head of the 

 short secreting trichome in Juglans calif ornica are relatively long, which is 

 a consistent character of the long secreting trichome as well, and it is this 

 circumstance which makes advisable the comparison of the lengths of the 

 heads in both pure species and hybrids, although other measurements have 

 also been made. The measurements on the length and the diameter of 

 the heads, as well as the lengths of the entire short secreting trichomes, 

 together with notes on the positions occupied by the trichomes, are pre- 

 sented herewith. 



The lengths of the heads of the short secreting trichomes are greater for 

 trichomes which are on the veins than for those which occur between them. 

 The measurements, in /*, are: length of heads, on veins, 35.7, 33.6, 27.3, 

 29.4, 27.3, 27.4, 27.3, 33.6, 33.6, 33.6, 33.6, 29.4; diameters of the same 

 heads, respectively, 25.2, 23.1, 29.4, 25.2, 27.3, 29.4, 23.1, 31.5, 25.2, 25.2, 

 29.4, 27.3; length of heads, between veins, 27.3, 21.0, 25.2, 29.4, 25.2, 

 29.4; diameters of the same heads, 25.2, 25.2, 25.2, 25.2, 25.2, 29.4. The 

 heads from trichomes on the veins average 30.9 /*, in length and 26.8 p in 

 diameter. The average lengths of heads from between the veins is 26.2 p- 

 and they average 25.9 p- in diameter. The heads of trichomes on the veins 

 show a variation in length of 13 per cent from the average; those between 

 the veins, a departure of 16 per cent from the average. The variation 

 from the average in diameter for the two series is respectively 13 and 8 

 per cent. 



Although it is recognized that the small number of measurements lessens 

 the value of the results in any instance, as a whole the number of measure- 



