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1909] CURRENT LITERATURE 235 
In D. longifolia there are 40 chromosomes in the nuclei of the sporophyte and 
_ 20 in those of the gametophyte, while in D. rotundifolia the numbers are 20 and 
Io respectively. The chromosomes of D. rotundifolia are somewhat smaller, as 
well as less numerous. The behavior of the chromatin in a hybrid between two 
such forms is naturally of some importance. 
In the hybrid, called D. obovata, the nuclei of the sporophyte show regularly 
30 chromosomes, the anticipated number, but in the nuclei of spore mother cells 
the condition is unique. At the metaphase of the heterotypic mitosis in the pollen 
mother cell there appear 10 double chromosomes, presumably resulting from the 
pairing of 10 chromosomes of D. longifolia with the 10 of D. rotundifolia. Besides, 
there are 10 smaller single chromosomes, presumably belonging to D. longifolia. 
These 10 smaller chromosomes are irregularly distributed; some enter the daugh- 
ter nucleus at the close of this mitosis, while others remain in the cytoplasm and 
may organize small nuclei, as in the well-known case of Hemerocallis. The 
behavior at the second mitosis is similar. The four spores of the pollen tetrad 
Stick together, so that it is possible to determine the entire number of chromo- 
Somes in the four nuclei. Counting the chromosomes in the four nuclei and 
including those of the dwarf nuclei, the number is about 60. In any given spore 
the number ranges from ro to 15, with 14 the most frequent. In a preliminary 
Paper, ROSENBERG concluded that two of the spores of a tetrad belonged to D. 
longifolia and two to D. rotundifolia. This conclusion is now withdrawn, and 
differences in the size of spores is attributed to differences in the number of chromo- 
somes. Sometimes a generative cell is formed, but usually the contents of the 
Spore begin to disorganize before this stage is reached. At the time of shedding, 
the pollen grain has a normal exine, but the contents are usually dead. 
In the formation of four megaspores from the mother cell the behavior is very 
similar to that just described. Occasionally, there is a well-developed embryo 
Sac, but in most cases disorganization begins before the four-nucleate stage 1s 
reached. 
ROSENBERG crossed the hybrid D. obovata with D. longifolia, and while usually 
there was no result, he obtained a few embryos. These contained at least 33 
chromosomes, and in one case 37 were counted. The theoretical number would 
The principal conclusions are (1) that the chromosome is an individual one 
of the cell, and (2) reduction of chromosomes is brought about by a fusion of the 
chromosomes of the two parents.—CHARLES J. CHAMBERLAIN. 
of Alchemilla. In addition to finding that the mildew on Alchemilla is 
confined to species of this genus, he also claims to be able to distinguish 
minor biological species” within this genus of host plants. For example, conidia 
a 
*Srerver, J. A., Die Spezialization der Alchemillen-bewohnenden Sphaerotheca 
Humuli (DC.) Burr. Centralbl. f. Bakt. etc. 212:677-726. 1908. 
