IQOS 



A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 1828. — Orobanche elatior. Emergent inflorescence. 



species occur in Britain, among which Lathraea and Orobanche are the best 

 known. Lathraea sqiiamaria (Toothwort) (Fig. 1829) occurs as an obhgate 

 parasite on the roots of Hazel, Ehii, Beech and other trees. It has a thick 

 stem which is covered below by fleshy scale-leaves. These scales are hollow 

 and contain a labyrinthine cavity opening to the exterior by a small pore on 

 the lower surface near the point of attachment. Secretory glands line this 

 cavity and it has been suggested that it may function to catch insects and 

 that previous to its parasitic life the Toothwort was an insectivorous plant. 

 There is no positive evidence for this, however. The flowers are borne on 

 the end of racemose inflorescences and are brownish white in colour with 

 purple bands. These flowers are all twisted round to one side of the 

 inflorescence, in the direction of the strongest light. The flowers are proto- 

 gynous and, in the first stage, the four stamens are curled up with their 

 anthers lying inside the lower lip of the corolla (Fig. 1830), while the yellow 

 stigma occupies the centre of the flower. In this stage the flowers are 

 pollinated by humble bees. Later the stigmas shrink and the centre of the 

 flower is occupied by the stamens, while the corolla tube elongates to double 

 its length. Cross-pollination is therefore elTected, as the bees search the 



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