8 



HEREDITY AS ILLUSTRATED BY TRICHOMES. 



The club-shaped trichomes were not so abundant as in the other pure 

 species. None were found on the lower surface of the leaf, either upon or 

 between the veins, and none on the stem. The following' measurements, 

 in ^. were made of club-shaped trichomes on the capsule: 96.6, 121.8, 

 134.4, 134.4, 147.0, 163.8, 168.0. The average length was 138.0/*. 



The pear-shaped trichomes occur on the lower surface of the leaves, on 

 the stem, and on the capsule. Other than being somewhat smaller in size 

 they are like those of Oenothera lamarckiana. Trichomes between the veins 

 on the lower surface of the leaves were found to have the following' lengths, 

 in/*: 23.1, 25.2, 25.2, 29.4, 29.4, 29,4, 33.6, 33.6, 33.6, 33.6, 35.7, 35.7, 39.9, 

 39.9, 42.0. The trichomes between the veins average 32.5 p in length. On 

 the veins the trichomes gave the following measurements, in m: 25.2, 31.6, 

 33.6, 33.6, 33.6, 33.6, 35.7, 37.8, 37.8, 37.8, 37.8, 39.9, 42.0, 42.0, 46.2. 

 The average length of the pear-shaped trichomes on the veins was found 

 to be 36.5 t x . The following measurements, in /*, were derived from tri- 

 chomes on the stem: 29.4, 29.4, 29.4, 31.5, 33.6, 33.6, 33.6, 33.6, 33.6, 

 33.6, 33.6, 35.7, 35.7, 35.7. The trichomes on the stem average 33.4 p in 

 length. On the capsule the measurements, in /*, were: 27.3, 29.4, 29.4, 

 31.5, 31.5, 31.5, 33.6, 33.6, 33.6, 33.6, 33.6, 35.7, 37.8, 37.8, 3.78. The pear- 

 shaped trichomes of the capsule average 33.2 m in length. The relation of 

 the pear-shaped and club-shaped trichomes to the areas where they occur 

 is shown in table 2. 



Table 2. Relation of the trichomes of Oenothera cmciata to the 

 position on the plant where found. 



In comparing the lengths of the pear-shaped trichomes of the two species 

 we find that those of Oenothera cruciata are smaller wherever found than 

 those of Oenothera lamarckiana, but that in both species the trichomes arc 

 of variable length. The longest trichomes, with hardly an exception, occur 

 in the region of the veins of the leaf, and the shortest occur between the 

 veins of the leaf. In both species, also, the trichomes of the stem and of 

 the capsule are, as a rule, intermediate in length. The absence of club- 

 shaped trichomes from the leaf and the stem of Oenothera cruciata precludes 

 a comparison of this trichome in the two plants, but it is significant that the 

 trichomes of this type on the capsule of Oenothera cruciata are smaller than 



