FERTILISATION. 43 



on the Carpathians, on the Pyrenees, on the Sierras of California, and 

 even in Greenland. On the Alps, amongst the materials which 

 constitute the dust, pollen grains of Conifers occur with great frequency 

 especially those of the Fir (Picea excelsa), the Arolla (Pinus Cembra), 

 and the Mountain Pine (Pinus mcmtana). These pollen grains have 

 been swept up into the high Alps by storms and soon become partially 

 decayed."* 



In all the material investigated by Professor Kernel 1 red-snow cells 

 were found mixed with pollen grains of these Conifers. 



FEKTILISATIOK 



Tin-: essential facts of fertilisation in Taxads and Conifers, viz., the 

 fusion of the male sexual cell contained in the pollen grain with 

 the female sexual cell within the ovule, are the same as in all 

 flowering plants, but the apparatus by which it is effected, as shown 

 in the foregoing section, is much simpler. In Great Britain the 

 fertilisation of Taxads and Conifers usually takes place in May, 

 earlier or later according to the season. At that period the pollen 

 is ripe and the scales of the ovuliferous flowers, although for the 



_ 



Fig. -JS. Anther of Pinus Larido : 3, side 4, dorsal and 5, top-view. 

 Magnified six diameters. Pollen grains x 200. 



most part closely imbricated or appressed when first developed, 

 separate sufficiently to afford safe and easy access to the pollen 

 grains wafted to them by the wind. 



The structure of the pollen grains is essentially the same throughout 

 the Taxacese and Coniferse, but there is a slight difference in size and 

 in the number of contained cells in the different genera. To the naked 

 ey<- the pollen grains appear like dry homogeneous dust, but under the 

 microscope they are found to be not simple bodies, but composed of 

 distinguishable parts. They are spherical or egg-shaped; each grain 

 is made up of two, three or more cells enclosed by a cell-wall which 

 consists of two layers, a thinner outer yellowish layer termed the extine 

 (analogous to the exospore of the spores of ferns and other cryptogams), 

 and an inner colourless thicker layer termed the .intine (analogous to 

 the endospore of ferns, etc.).f The entire inner space of the pollen 

 grain is at first filled with granular protoplasm which afterwards 

 divides into two portions, a larger and smaller, separated from each 



Reiner's " Natural History of Plants," Oliver's Translation, Vol. I. pp. 37, 38. 



t In the Cupressirieae the pollen sacs and their contents bear a still more striking 

 resemblance to the corresponding organs of fructification in Lycopodium, Selaginella, etc. 

 (The sporangium and its contained microspores). 



