106 PROTECTION OF POLLEN. 



plants, so also in that of the multitude of plants which germinate and flower on 

 dry land, if the pollen happens to fall into the water or is purposely kept immersed, 

 it is destroyed. 



It is thus the fact that the pollen of Phanerogams, with the exception of 

 about fifty species, of which the Grass-wracks may be taken to be the type, is 

 injured by prolonged immersion or subaqueous transport. This obviously suggests 

 an inquiry as to the reason of the hurtful action of water upon cells which require 

 an especial abundance of liquid materials for the development of the pollen-tubes. 

 There is, however, a great difference between the absorption of pure water and 

 the absorption of the liquid substances yielded by stigmas. A pollen-cell deposited 

 upon a stigma gradually takes up the liquids there available, and the pollen-tube 

 pushes out comparatively slowly. If, on the other hand, the pollen-cell is put into 

 water, or is in nature so wetted by rain or dew as to be practically immersed in a 

 water-bath, absorption of water takes place almost instantaneously; the intine is 

 pushed out wherever no resistance is offered by the extine, and in a moment the 

 pollen-cell swells up. Such a process cannot properly be called a development 

 of the pollen-tube. No real growth can take place in so short a time, and what 

 has occurred is simply an expansion of the intine and a smoothing out of the folds 

 which have hitherto lain tucked in. Frequently, indeed, the limits of elasticity are 

 exceeded; the projecting part of the intine bursts, and the spermatoplasm flows out 

 into the water in the form of a finely granulated, slimy mass. In that event the 

 pollen-cell is destroyed, and comes to nothing. But even if the intine does not 

 burst, the pollen undergoes such complete alteration through the rapid absorption 

 of water that its protoplasm loses the power of fertilization. It seems as if the 

 protoplasts inclosed in pollen-cells, subjected to prolonged immersion, were literally 

 drowned. Thus much is certain, that the immense majority of pollen-cells perish 

 under water, and that even if wetted they incur great risk of destruction. This 

 danger, which may be of daily occurrence in case of rain or heavy dew, has to be 

 avoided. In order to preserve the pollen fit for use it must be secured by 

 protective apparatus against the injurious effects of moisture, especially against 

 atmospheric deposits; it must be able to develop under conditions from which this 

 factor — ^in so far as it is harmful — is, generally speaking, excluded. 



In regions where there is a regular alternation of rainy and rainless seasons — 

 in the llanos of Venezuela, the Brazilian campos, the dry districts of India and 

 the Soudan, above all, in the parts of AustraKa to the south of the tropic where 

 the rainfall is limited to the winter and afterwards ceases for months — the climate 

 itself indirectly affords security to the pollen against risk from water; or, in other 

 words, any apparatus to protect from rain the pollen of plants which flower in 

 rainless seasons would be superfluous. The trees which wave above the grass of 

 the wonderful savannahs of Australia, as also the numerous dry and rigid shrubs 

 which belong to the adjacent " scrub ", do not flower until the rainy season is over, 

 when the flowers do not run any risk of being drenched with rain. In the absence 

 of the danger the necessity for any direct means of defence against it also 



