Pollen tubes of maize enter the silk intercellularly via multicellular hairs located on two opposite sides of the silk or epidermis cells of the silk proper. The silk contains two vascular bundles. A strand of "transmitting tissue” is associated with each bundle, separated from xylem elements by one parenchyma layer. The pollen tubes grow intercellularly towards the "transmitting tissue” and then between the cells of this tissue down the silk. The diameter of the pollen tubes ranges between 6-13 pm but increases to 26-55 pm at the enlarged section of the tube.