244 MORPHOLOGY. 



This usually occurs, either in the mother cell of the spores or in 

 the divisions of its nucleus, at the time the spores are formed. In 

 the mother cells a sort of pseudo-reduction is effected by the 

 chromatin band separating into one half the usual number of nu- 

 clear segments. So that in lilium during the first division of the 

 nucleus of the mother cell the chromatin band divides into twelve 

 segments, instead of twenty-four as it has done throughout the 

 sporophyte stage. So in podophyllum during the first division in 

 the mother cell it separates into eight instead of into sixteen. 

 Whether a qualitative reduction by transverse division of the 

 spirem band, unaccompanied by a longitudinal splitting, takes 

 place during the first or second karyokinesis is still in doubt. 



476. Significance of karyokinesis and reduction. The pre- 

 cision with which the chromatin substance of the nucleus is di- 

 vided, when in the spirem stage, and later the halves of the 

 chromosomes are distributed to the daughter nuclei, has led to the 

 belief that this substance bears the hereditary qualities of the 

 organism, and that these qualities are thus transmitted with cer- 

 tainty to the offspring. In reduction not only is the original 

 number of chromosomes restored, it is believed by some that 

 there is also a qualitative reduction of the chromatin, i.e. that 

 each of the four spores possesses different qualitative elements of 

 the chromatin as a result of the reducing division of the nucleus 

 during their formation. 



The increase in number of chromosomes in the nucleus occurs 

 with the beginning of the sporophyte, and the numerical reduc- 

 tion occurs at the beginning of the gametophyte stage. The 

 full import of karyokinesis and reduction is perhaps not yet 

 known, but there is little doubt that a profound significance is to 

 be attached to these interesting phenomena in plant life. 



377. The gametophyte may develop directly from the tissue 

 of the sporophyte. If portions of the sporophyte of certain of 

 the mosses, as sections of a growing seta, or of the growing 

 capsule, be placed on a moist substratum, under favorable condi- 

 tions some of the external cells will grow directly into protonemal 

 threads. In some of the ferns, as in the sensitive fern (onoclea), 



