334 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
the chalaza. In the other tissues of the ovule, growth ceases and the cell 
contents display a somewhat lighter staining reaction than normally. 
Changes in the ovaries are less likely to involve all germ cells than 
those which occur in the anthers. In the case of congenital changes which 
involve mainly the pollen and appear at a late stage in the development 
of the floral organs, many ovules may escape and develop into seed if the 
environmental conditions are favorable and if suitable cross-pollination is 
provided. 
Summary 
1. The potato is an unfavorable subject for cytological study on account 
of the small size of the cells and the degenerative changes which precede 
the shedding of the blossoms. These difficulties have deterred investigators 
from carrying out the study. 
2. The development of the flower and of the germ cells does not show 
any marked differences from cases previously described for related plants. 
3. Degenerative changes in the anther contents show decided differences 
according to the stage at which degeneration begins. Changes which 
occur at early stages of development appear to be due to unfavorable 
climatic or environmental conditions. The disintegration of nearly mature 
pollen grains appears to be the result of hereditary pollen sterility and does 
not interfere with the normal anthesis of the blossoms. 
4. Degenerative changes in the ovules and embryo sac appear to result 
from unfavorable environment and may occur at any stage. They are much 
more uniform in character than those found in the anther. 
5. Varieties which produce no viable pollen may set fruit and produce 
seed, provided environmental conditions are not such as to induce de¬ 
generative changes in the embryo sacs, and provided the blossoms are 
promptly crossed by a variety producing viable pollen. 
EXPLANATION OF PLATES 
Plate XXV 
Fig. 1. A, Archesporial cells in anther. These cells are angular and arranged in 
groups. They have dense, deeply staining protoplasm and large nuclei. T, Tapetum. 
N, Nutritive cells. These tissues have to do with the nutrition of the sporogenous^tissue 
and contain conspicuous vacuoles filled with cell sap. 
Fig. 2. P.M., Pollen mother cells developing from the archesporium. T, Tapetum. 
N, Nutritive cells, usually containing two nuclei each. 
Fig. 3. Development of tetrads from pollen mother cells. 1, Pollen mother cells. 
2, Spireme and synapsis stages, j, Prophase, nuclear membrane dissolved. 4, Metaphase 
of heterotypic division. 5, Anaphase of same. 6, Telophase of same. 7, Daughter cells 
of heterotypic division. 8, Metaphase of homoeotypic division, p, Late anaphase or 
telophase of same. 10, Daughter cells of homoeotypic division, u, Formation of con¬ 
strictions which separate the microspores. 12 , Microspores formed but enclosedJn]original 
wall of pollen mother cell. 13, Two cells formed by the heterotypic division, homoeotypic 
division omitted. 
Fig. 4. Megaspore surrounded by the tissue of the ovule and the developing in¬ 
tegument. 
Lookout Mountain. X 680. 
