CELL-NUCLEUS—FERTILISATION 241 
fertilisation recurs meiosis is neveromitted,!and 
this is true for animals as well as for plants. 
The ordinary course of life histories has been 
developed long after sexuality and meiosis 
appeared, and has progressed independently, 
and on different lines in different groups. 
Sometimes, as in the higher plants, the stages 
of the life history are more or less obviously 
connected with these nuclear cardinal points, 
at other times the relation is not so evident. 
For example, it may happen, as in many of 
the flowering plants, that the two stages in 
the life history so well separated and analysed 
in the fern, become curtailed. This happens 
when the cell which should give rise, by the 
two divisions, to four spores, cuts the process 
short, grows, and itself becomes the spore 
without any division. Such a short cut is 
taken in certain of the sporangia (ovules) of 
a lily, orchis, and many other plants. But 
meiosis is not cut out. It supervenes at the 
very next divisions which follow the omitted 
stages during which it would normally have 
been effected. 
As we advance to types of plants above the 
ferns we find the life history becoming more 
complicated and less diagrammatically clear. 
The principle which underlies the complica- 
tion is, however, a simple one; it consists 
in a provision for giving the sexually produced 
embryo an advantageous start in life. 
1 The occasional anomaly reported for certain mosses 
requires further investigation. 
Q 
