. Botany of the living plant. Botany. Fig. 144. Median section of a young plant of Orobanche seated upon the root of its host. (After Hovelacque.) ( x 20.) •\ IRREGULAR NUTRITION 193 and cortex, thus tapping both storage and conducting tissues. Where the sucker impinges upon a vascular strand a continuous xylem- connection may be estabhshed ; in the phloem also a close relation of the sieve- tubes of the parasite with those of the host has been shown. The Broomrape {Orobanche), and the- Toothwort {Lathraea) are further examples of parasites with complete physiologi- cal dependence. Both of the
. Botany of the living plant. Botany. Fig. 144. Median section of a young plant of Orobanche seated upon the root of its host. (After Hovelacque.) ( x 20.) •\ IRREGULAR NUTRITION 193 and cortex, thus tapping both storage and conducting tissues. Where the sucker impinges upon a vascular strand a continuous xylem- connection may be estabhshed ; in the phloem also a close relation of the sieve- tubes of the parasite with those of the host has been shown. The Broomrape {Orobanche), and the- Toothwort {Lathraea) are further examples of parasites with complete physiologi- cal dependence. Both of these are root- parasites, with attachment to the host by haustoria, which penetrate the tissues. The Toothwort which infests the roots of Haze! is classified in the Scrophulariaceae, close to the Eyebright and Yellow Rattle, which are themselves partial root-parasites. But it differs from them in having become entirely dependent physiologically upon its host. The leaves are still represented on the underground shoot, and their curiously reduced and altered form gives rise to the name of Tooth-Wort. But the flowering shoot rises above ground, displaying flowers with structure characteristic of the Family. The Broom-rapes (Orobanche), which attack various plants, woody or herbaceous, are closely related to Lathraea. They show a greater modification of the shoot, which attaches itself on germination to the root of the host, developing a brown tuberous body, without leaves, and shut off from the light. By means of a sucker it burrows with a broad surface into the root of the host plant, and establishes a close relation- with its conducting tissues (Fig. 144). The flowering shoot with its brownish leaves rises above ground, be? ring numerous flowers. Their structure shows that it is a form related to the Toothwort, but its vegetative system is still more reduced, leaves being absent from the base of the tuber. This reduction runs parallel to but distinct from that seen in Convolvulu
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
