CELL-NUCLEUSFERTILISATION 245 



developed within it a very rudimentary 

 structure which it is possible to trace back 

 to an extremely reduced prothallus. The 

 pollen grain presently begins to put forth a 

 tube which grows into the tissue of the stigma, 

 feeding, like a fungal hypha, on the juices it 

 contains. The tube grows down through the 

 intervening tissue of the style into the cavity 

 of the ovary. When it reaches this it is 

 attracted to the tips of the ovules, and enters 

 one of them by way of a little pore (the 

 micropyle), burrowing through an intervening 

 tissue of the sporangial (i. e. ovular) wall that 

 may be present, until it reaches the spore. 



Meanwhile, from the body of the pollen 

 grain the essential structures above alluded 

 to have entered into the tube. Two sperms 

 are developed, but they are not provided 

 with locomotory cilia. They are finally dis- 

 charged into the cavity of the spore, when 

 they at once lose all cytoplasmic invest- 

 ment, and appear as naked nuclei, somewhat 

 vermiform in appearance. They pass through 

 the protoplasm, which is contained in the 

 spore (or embryo-sac as it is often called), 

 apparently by autonomous movement, and 

 one of them approaches, and finally fuses with, 

 the egg. The other one fuses with a remark- 

 able pair of nuclei which are found near the 

 centre of the egg, and the nucleus resulting 

 from the latter fusion is responsible for the 

 production of the nutritive matter that 

 later on fills so many seeds and grains (e. g. 



