284 The Living Plant 



swim of themselves. But in all cases the principle is the same; by 

 suitable structures and accessory adjustments and adaptations, 

 the male cell is brought into contact with an egg- 

 cell, to which it passes over its nucleus, with more 

 or less cytoplasm; the two nuclei then fuse, and 

 thus is formed a fertilized egg-cell from which the 

 new individual develops. 



In following this process it becomes evident that 

 the object of all the elaborate machinery of fertili- 

 FIG. 98. A typi- zation is to secure the union of the male and female 



cal pollen grain , . . , . , ,. i_ i_ 



(of Tradescan- nuclei, for that is the one feature which is com- 

 ticai ScTion and P letel y constant throughout. This of course raises 

 highly magni- the question as to what the nucleus actually is. 



fied, showing, on 



the left, the cell As our chapter on Protoplasm showed, every nu- 



which produces , *. n i 



the male, or cleus contains a certain peculiar matter called 



(Copied C f rm chromatin, which, ordinarily scattered throughout 

 strasburger's the nucleus, collects itself at times into a definite 

 number of rod-like structures called chromosomes 

 (figure 101). The evidence seems to show beyond question, 

 though the method thereof is in doubt, that these chromosomes 

 embody within themselves the characteristics of the parent 

 plants, (or, constitute the working plans or patterns thereof, 

 so to speak), and in such manner as to exert control over the 

 development of offspring, and ensure that new individuals shall 

 grow up in resemblance to those that produced them. Now 

 in fertilization each nucleus contributes its chromosomes, so that 

 the nucleus of the fertilized egg-cell contains a double number 

 derived equally from both parents (figure 100). The significance 

 of this fact, however, becomes apparent only as we follow the 

 behavior of the chromosomes during the development of the 

 fertilized egg-cell into an adult plant; for in such development, 

 the egg-cell first divides across into two, and then its parts into 

 two, and so on until the whole plant is completely grown. Now 

 in the first division each one of the chromosomes, both those 



