Morphological characteristics of trichomes of primin-secreting and primin-free cultivars in Primula obconica

A comparison of the trichome types was made by the Craven test and microsco pic observation between primin-secreting and primin-free cultivars of Primu la obconica. 1. All cultivars were classified into two groups according to the lengths o f trichomes. Group one had trichomes (Fig.1, A similar to D) whose lengths were 150 mu m or less, whereas group two was represented by those with tric homes exceeding 1mm (Fig.1, E). Moreover, the trichomes of group one was fu rther classified into four types from the characteristics of the tips, e.g. , A : red tip; B : colorless tip; C : yellow tip and D :tip with crystalliz ed substance (Fig.1, A,B,C and D, respectively). 2. The trichomes of B, C, and D types were observed both on the primin-secr eting and free cultivars but those of A type were observed only on the prim in-secreting cultivars. By the Craven test, only the trichome of A type sec reted primin at its apex. 3. The distribution density of A type trichome (primin-secreting) was highe r on the basal part of the midrib in leaves and on the calyx and peduncle i n flower clusters, than in other parts of leaves and newer clusters. Thus, it should be possible to select primin-free plants by avoiding the pl ants with red tipped trichomes on midrib of young leaves, calyx and peduncl e of newer clusters.