THE CARPEL 



201 



of the middle lamellae and float free in a mucilaginous fluid (Fig. 79E, 

 F, H). This condition has been considered rare — "found in orchids only" 

 — but was long ago reported for many taxa. 



Function of the Transmitting Tissue. The discovery, in 1823, of pollen 

 germinating on the stigma aroused renewed discussion of the mystery 

 of the method of fertilization. Two theories had been held in the pre- 



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MUmi^ 



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Fig. 79. Transmitting tissue. A, Vcrhascum vermile, transverse section of placental 

 tissue, parenchyma cells swollen and filled with starch; B, Pittosporum sinensc, 

 papillose surface of ovary wall near ovules; C, Solamtm glaucophijllum, transverse 

 section of surface of placenta, epidermal cells filled with starch; D, Riibiis odoratus, 

 transmitting tissue of the carpel margins at top of ovary; E, cross sections of pollen 

 tubes filled with starch grains in the gelatinous substance formed from the break- 

 down of the middle lamellae of the transmitting tissue; F, Deherainia smaragdina, 

 cross section of part of the style showing stylar canal filled with mucilage in which 

 the pollen tubes run; G, Cheirantlius cheiri, transverse section of ovary, showing 

 central transmitting tissue; H, Fumaria major, cross section of stylar canal filled with 

 granular mucilage and lined with a conducting epidermis against which the pollen 

 tubes lie. {After Capus.) 



ceding century: that the "fertilizing dust" (pollen) contained an "esprit 

 vohtil," which entered the vascular tissue of the stigma, passed down 

 to the placenta, entered the ovules, and fertilized the "embryo"; that 

 the pollen grains themselves "descended" into the ovary through open 

 stylar canals (then believed to occur in all plants) and formed the 

 "basis of the embryo." The discovery that, in many plants, the stylar 

 canals were closed completely, or for part of their length, and that the 



