6 HEREDITY AS ILLUSTRATED BY TRICHOMES. 



The club-shaped trichomes, as well as the pear-shaped ones, are gland- 

 ular, and hence living - . Both are less variable in size than the awn-shaped 

 trichomes and both have lengths characteristic of each species. The lead- 

 ing characters of the glandular trichomes are sufficiently shown in fig. 1 

 and do not require further description in this place. 



OENOTHERA LAMARCKIANA. 



In the pure parent Oenothera lamarckiana, the three kinds of trichomes 

 above described are to be found on the lower surface of the leaves, on the 

 stem, and on the capsule. The variation of the awn-shaped trichome, which 

 was referred to above, may be shown by the following measurements, 

 expressed in m: ventral surface of the leaf, 163.8, 168, 191.2, 202.6, 222.2, 

 223.1, 244.6, 248.8, 265.6, 306.6, 344.4, 399.0, 420.4. The trichomes above 

 measured were selected at random; the following measurements are of tri- 

 chomes which were in the region of the veins of the leaf, expressed in /: 

 126.0, 231.0, 239.4, 252.0, 252.0, 336.0, 399.0, 420.0, 453.6. On the stem 

 the measurements were 126.0, 159.6, 176.0, 269.6, 387.2, 440.0, 721.6, 

 756.8, 844.8, 880.0, 915.0, 1144.0, 1196.8. On the capsule these trichomes 

 were less numerous but were all relatively long, as the following" measure- 

 ments, in /*, indicate, 844.8, 897.6, 915.2, 922.8, 968.0, 1003.6, 1073.6, 

 1073.6, 1144.0, 1196.8. 



The club-shaped trichomes occur also on the ventral surface of the leaves, 

 on the capsule, and on the stem. This type of trichome is more uniform in 

 size in any given area, as between the veins or on the veins of the leaf, 

 than the awn-shaped trichome, and also the trichomes of different areas 

 are more nearly the same size than those of the other (awn-shaped) type. 

 This is also true, and perhaps more consistently so, of the pear-shaped 

 trichomes, the measurements of which will be given below, from which 

 circumstance a study of them as inheritable qualities is of value. The fol- 

 lowing measurements, in /*, were made of the club-shaped trichomes taken 

 from the lower leaf-surface and between the veins: 168.0, 176.4, 180.6, 

 184.8, 189.0, 189.0, 197.4, 201.6, 210.0, 227.0, 231.2, 231.0, 247.8, 252.0, 

 253.0. Trichomes on the veins measured as follows, in p: 168.0, 168.0, 

 180.6, 189.0, 191.2, 201.6, 205.6, 211.0, 211.0, 231.0, 252.0. Club-shaped 

 trichomes on the stem had the following lengths, in ^: 131.2, 172.2, 176.4, 

 180.6, 180.6, 201.6, 210.0, 210.0, 222.6, 248.8. On the capsule these tri- 

 chomes measured as follows, in /*: 155.4, 163.8, 176.4, 189.0, 205.6, 211.0, 

 222.6, 231.0, 235.2, 252.0, 252.0. The average lengths of the club-shaped 

 trichomes for the given areas are as follows: lower surface of leaf, on vein, 

 200.08 p-\ between veins, 209.2 /*; on stem, 193.4 /"; on capsule, 208.5 /*. 



Pear-shaped trichomes were studied on the ventral surface of leaves, on 

 the stem, and on the capsule. The following measurements, in /*, give the 



