Studies on the Ontogeny of the Dwarf Mistletoes, Arceuthobium. II. Homology of the Endophytic System

Studies on the Ontogeny of the Dwarf Mistletoes, Arceuthobium. III. Development of the Inflorescence

“…THE DWARF mistletoe plant consists of 2 morphologically distinct parts: an extensive haustorial system within the host, and an aerial portion (the inflorescence) of spike-like cymes which bear either staminate or pistillate flowers. Whereas the anatomy of the haustorial system of several species of dwarf mistletoes has already been described in considerable detail (Sohns-Laubach, 1867;Heinricher, 1923;Thoday and Johnson, 1930;Cohen, 1954;Kuijt, 1960;Srivastava and Esau, 1961; and others), details of inflorescence development are fragmentary and imperfectly known (Thoday and Johnson. 1930;Cohen, 1954;Kuijt, 1960).…”

“…This is not the case in Arceuthobium. Here the shoot apex of the embryo is rudimentary; it eventually dies and decays along with the remaining external portion of the seedling after the host is infected (Cohen, 1963b). The inflorescence in Arceuthobium is therefore an adventitious structure which originates in the endophytic system located within the host plant rather than from the shoot apex of the seedlinz,…”

“…INITIATION OF THE INFLORESCENCE-Buds which give rise to inflorescences (the aerial shoots) are formed in the peripheral region of the endophytic system (Thoday and Johnson, 1930;Cohen, 1954). They first appear either as small meristematic protuberances on the outer surface of cortical strands or at the ends of short branches.…”

“…In the condensed system, represented by A. campylopodum Engelm., clusters of buds are formed radiating from a major center of infection [Vol. 52 (Cohen, 1954). The endophytic system is restricted to an elliptical zone and its host develops a pronounced fusiform hypertrophy.…”

“…52 as an adaptation to parasitism. But most of these specialized structures are unique to the dwarf mistletoes and, therefore, cannot be evaluated as to whether they are primitive or advanced by comparison with other angiosperms (Cohen, 1963b). It is impossible to say whether the endophytic system, for example, is actually a primitive absorptive organ or whether it represents a once highly evolved root or stemlike structure which has regressed to a state of structural simplicity as an adaptation to parasitism.…”