1024 ELLIOT ROWLAND DOWNING 
always to occur with definite relation to the alternation. The 
gametophyte, the plant that gives rise to the sexual elements, 
bears the reduced or haploid number of chromosomes. The 
sporophyte, the generation that produces the asexual spores, has 
the diploid or somatic number. Reduction occurs at the time 
the asexual spores are produced. So generally is this true, that 
for a time in many botanical papers, the presence of the diploid 
number of chromosomes was looked upon as a criterion that the 
cell possessing this number belonged to the sporophyte; or is a 
gametophyte cell if it has the haploid number, and the conclusion 
reached in a study of the archegoniates is forced, on a priori 
grounds, to cover the thallophytes as well. Thus Yamanouchi 
speaking of Williams’ work on Dictyota says ‘“‘The fertilized 
egg nucleus gives rise to an asexual plant with double the number 
of chromosomes and consequently a sporophyte generation.” 
(Bot. Gaz., vol. 42: p. 481). And again, quoting from Davis, 
‘Morphologically we can distinguish sporophyte plasm from gam- 
etophyte plasm by the double number of the chromosomes.”’ 
(Am. Nat., vol. 39: p. 456). 
In subjecting this life history [of Coleochaete] one of the green algae 
to what is regarded as a critical test of the two generations it has been 
discovered that this special spore-producing body is not a sporophyte. 
The test has to do with the number of chromosomes in the nucleus, a 
number which is definite for each plant species. The chromosomes are 
doubled in number by the fusion of the sperm and egg to form the oospore; 
and this means that in some other point in the life cycle the number must 
_ be reduced again. Accordingly the sporophyte, which arises from the 
oospore, is characterized by the double or 2x number of chromosomes in 
its nuclei; and the gametophyte, which gives rise to the gametes, is char- 
acterized by the reduced or x number of chromosomes. Text book of 
Botany, Coulter, Barnes, Cowles; vol. 1, p. 32. 
Alternation and reduction independent 
Recently, however, cytological studies on botanical material 
have thrown serious doubt on this conception. Reduction and 
the alternation of generations are, even in plants, independent 
phenomena. I shall briefly cite three lines of evidence in proof 
of this proposition. The few papers to which I refer will give 
references to abundant literature. 
