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A TEXTBOOK OF THEORETICAL BOTANY 



micropylar and chalazal, though not infrequently, as in Lobelia and Globu- 

 laria, both may be formed in the same ovule (Fig. 1336). 



B 



Fig. 1336. — Globiilan'a cordifoUn. A, Chalazal haustorium with a 

 lateral caecum. B, Haustorial elongation of basal cells of the 

 endosperm. C, 0\ule in longitudinal section showing haus- 

 toria de\eloped at both ends. {After Billings.) 



Micropylar haustoria, though often extensive, are generally simple in 

 organization. They mostly consist of unicellular outgrowths, in which, as 

 they enlarge, free nuclear multiplication may take place, growing through 

 the micropyle and branching freely in a mycelial manner over the surface of 

 the ovule and the ovary wall or penetrating the tissue of the funicle or the 

 placenta. In the Labiatae the haustorium begins as an enlargement of the 

 apical end of the embryo sac, into which pass several endospermal nuclei. 

 The sac thus formed may enlarge very considerably and throw out branches. 

 Such is the case in Galeopsis, where a lateral outgrowth from the haustorial 

 sac penetrates the integument and reaches upwards to the apex of the ovarial 

 cavity. 



Another type of micropylar haustorium is formed by groups of cells 

 (Fig. 1337) from the micropylar portion of cellular endosperm, which en- 

 large upwards into the micropyle. Veronica (Fig. 1338) and Lobelia have 

 such haustoria, composed often of a pair of enlarged cells which have been 

 mistaken for large synergidae. Lateral outgrowths may be formed also in 

 this type of haustorium, e.g., in Byblis (Lentibulariaceae) where the lower 



