132 ANATOMY AND PHYSIOLOGY OF 



in which this forms but a very small part of the colossal style, or 

 in Lomatogonium, where the coherent borders of the carpellary 

 leaves consist of stigmatic substance along the whole of the ovary. 

 The pistil is incapable of fertilization, until after the secretion 

 of the above-mentioned viscid fluid upon the stigma, for though 

 the pollen-grains indeed adhere to the stigma from being more or 

 less glutinous, they cannot be any farther affected. But as soon 

 as this secretion has appeared, the germination of the pollen- 

 grains commences, often in a few minutes, in any case in a few 

 hours. The inner coat breaks through the outer in the form of a 

 cylindrical tube, which applies itself to the stigmatic papillae 

 (sometimes, as in Matthiola annua, penetrates into them), grows 

 downwards among them, and penetrates between the cells of the 

 conducting tissue. Ordinarily only one tube is emitted from each 

 grain, but in those grains which possess several pore4ike points 

 on their outer coat, and in which the portion of the inner coat 

 situated beneath those places always becomes developed into a tube, 

 one grain not unfrequently produces several tubes, the number 

 having been seen by Amici to amount to 20 — 30, The pollen-tubes 

 make their way, by continuous growth at their ends, through the 

 conducting tissue of the style into the ovary, attaining, in long- 

 styled plants, like Gaotus grandifiorus, for instance, a length 

 which may exceed the diameter of the pollen-grain several 

 thousand times. This considerable length alone, but still more the 

 circumstance that the wall of the pollen-tube is often exceedingly 

 thin in proportion to its cavity, shews that its formation does not 

 depend upon mechanical extension of the pollen-membrane, but 

 on a growth, the requisite nutriment for which is drawn from the 

 viscidfluid poured out among the cells of the conducting tissue. 



The rate at which the growth takes place varies very much 

 in different plants, and is not subject to any universal rule. The 

 first result of it is an attachment of the pollen-grain to the stigma, 

 so that it can no longer be readily wiped off* the latter. According 

 to Gartner, this often takes place in even half a minute, while, in 

 other cases, many hours may elapse (in Mirahilis and the Mal- 

 vacece, as many as 24 — 36). The growth of the pollen4ube down 

 the style likewise occupies very varied periods in different plants. 

 In many plants, several weeks pass before the pollen-tubes have 

 passed through a stjde only a few lines long, while in others, 

 even when the style is very long, a few hours suffice (6.g., in 

 Cactus grandifiorus and Golchicum). After the pollen-tubes 

 have penetrated the stigma, the secretion of the latter ceases, and 

 its tissue begins to die away, while the lower part of the pollen - 

 tube is still in a growing condition. The fovilla passes down- 

 wards in proportion as the tubes are elongated, so that the pollen- 

 grains collapse on the stigma soon after their application upon it. 

 The pollen-tubes being so long, the fovilla must certainly become 

 more and more considerably diluted by the absorbed fluid, jet it 



