Pollen tubes chemotropic factor

Recent investigations indicate that the failure to obtain a positive chemotropic response may be an artifact. Failure to observe chemotropism may result from interference by pollen tube growth inhibitors, a factor causing negative chemotropism, by inherent errors in the surface test method, by the existence of genetically controlled incompatibility systems, and by factors of age of tissues and other characteristics of the plants. 

Since the chemistry of the chemotropic factor is unknown, the mechanism of the chemotropic response can be explained only in anatomical terms. It is from this point of view that we will consider the meager speculations to be found in the literature. First, however, it is necessary to recognize the fact that a pollen tube grows at its extreme tip. According to Iwanami... 

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