76 THE EVOLUTION OF PLANTS 



produced in each pollen-tube; there is, however, 

 a striking exception in Microcycas, a most re- 

 markable plant of which scarcely anything was 

 known till it was rediscovered three years ago, by 

 the American botanist Caldwell, on the moun- 

 tains of Cuba; instead of being a little plant as 

 was supposed before, Microcycas turned out to be 

 a tree thirty feet high, with female cones a yard 

 long (figs. 4 and 5). The interesting point in the 

 reproduction is that each pollen-tube produces no 

 less than sixteen spermatozoids (fig. 7, A) a fact 

 which offers an interesting parallel to the condi- 

 tions in some of the Palaeozoic Seed-plants (Chap- 

 ter IV). In Microcycas the number of egg-cells is 

 extraordinarily large, as many as two hundred in 

 a single ovule, whereas from three to five is about 

 the usual number in other Cycads. 



After fertilisation more than one embryo may 

 go on developing for a time; in Microcycas there 

 may be a dozen or more. Sooner or later one gains 

 the upper hand, and is alone present by the time 

 the seed is ripe. The embryo is then embedded in 

 the endosperm, which always fills the stone of 

 the seed and is only used up when germination 

 takes place. An interesting point in Cycads is 

 that the embryo may scarcely develop at all till 

 the seed is sown, so that the apparently ripe seed 

 may contain no obvious embryo. It is common 

 in Cycads for there to be no resting-stage in the 



