Cross-pollination

The blooming of the vine had little significance to the grape-grower,
the blooming period being so late that grapes are seldom caught by
frost, until the discovery was made that many varieties of grapes are
unable to fertilize themselves, and that failure of crops of these
varieties was often due to the self-sterility of the variety. Until
this discovery, the uncertainty attending the setting of the grape in
these varieties was one of the discouragements of grape-growing.
Following investigations of the self-sterility of the tree-fruits, an
investigation of the grape showed that the vines of this fruit are
often self-sterile. This knowledge has in some degree modified the
planting of all home collections and has more or less affected the
plantings of commercial sorts.

Varieties of American grapes show most remarkable differences in the
degree of self-fertility. Many sorts fruit perfectly without
cross-pollination. Others set no fruit whatsoever if cross-pollination
is not provided for. Most varieties, however, are found in groups
between the two extremes, neither self-fertile nor self-sterile.
Figure 51 shows staminate and perfect clusters on one vine. Some
varieties show no variation in the degree of self-sterility or
self-fertility; others behave differently in regard to these
characters under different environment. Now and then the widest
variations are to be found in a variety in respect to self-fertility.

right, staminate; left, perfect.]

Following the lead of Beach at the New York Agricultural Experiment
Station, several workers have made careful studies of the
self-fertility of the grape, and now the cultivated varieties of
native grapes are divided into four groups in accordance with the
degree of self-fertility. Class I includes self-fertile varieties
having perfect or nearly perfect clusters; Class II includes
self-fertile varieties having clusters loose but marketable; Class III
includes varieties which are so imperfectly self-fertile that the
clusters are generally too loose to be marketable; Class IV includes
self-sterile varieties. The following is a list of commonly cultivated
grapes classified according to the divisions just given:

CLASSIFICATION OF GRAPES ACCORDING TO SELF-FERTILITY

CLASS I. Clusters perfect or varying from perfect to somewhat loose.

Berckmans
Bertha
Cottage
Croton
Delaware
Diana
Etta
Janesville
Lady Washington
Lutie
Moore Early
Poughkeepsie
Pocklington
Prentiss
Rochester
Senasqua
Winchell

CLASS II. Clusters marketable; moderately compact or loose.

Agawam
Brilliant
Brown
Catawba
Champion
Chautauqua
Clinton
Colerain
Concord
Dutchess
Early Victor
Elvira
Empire State
Fern Munson
Hartford
Iona
Isabella
Isabella Seedling
Jefferson
Jessica
Lady
Mills
Missouri Riesling
Perkins
Rommel
Triumph
Ulster

CLASS III. Clusters unmarketable.

Brighton
Canada
Dracut Amber
Eumelan
Geneva
Hayes
Lindley
Noah
Northern Muscadine
Vergennes

CLASS IV. Self-sterile. No fruit develops on covered clusters.

America
Aminia
Barry
Black Eagle
Clevener
Creveling
Eldorado
Faith (?)
Gaertner
Grein Golden
Hercules
Jewel
Massasoit
Maxatawney (?)
Merrimac
Montefiore
Requa
Salem
Wyoming

In the main, the cause of infertility, as with other fruits, is the
impotency of pollen on the pistils of the same variety. There are a
few cases in which pollen does not seem to be formed abundantly, but
these are very few. There are a few cases, also, in which the pistil
does not become receptive until after the pollen has lost its
vitality; these, however, are very few. In a greater number of cases
the pollen is found defective. However, dismissing all of these as the
exception, the rule is that self-sterility is due, as has been said,
to the lack of affinity between pollen and pistils produced on the
vines of some varieties.

Nature is helpful to the grape-grower in giving a guide to
self-fertility. The length of stamens is a fairly safe indication of
self-fertility. All grapes which are self-fertile bear flowers with
long stamens, although the latter are not a sure sign of
self-fertility, as a few varieties with long stamens are self-sterile.
On the other hand, short or recurved stamens are always associated
with complete or nearly complete self-sterility.

The remedy for self-sterility is inter-planting. Only the varieties
named in Classes I and II in the foregoing classification should be
planted alone. The sorts named in Classes III and IV must be planted
near other sorts which bloom at the same time in order that their
flowers may be cross-pollinated.

It is evident that the grape-grower must have some knowledge of the
relative time that grapes bloom, if he is to plant intelligently to
secure cross-pollination. The following table, taken from Bulletin 407
of the New York Agricultural Experiment Station, shows the blooming
time of grapes at that Station. Variations due to location and season
must be expected, but within the bounds of the regions in which these
grapes are grown variations will be slight. When this table is used
for other regions than New York, it must be borne in mind that the
farther south, the longer the blooming season; the farther north, the
shorter the season.

Blooming dates of grapes.

From three years' records, the average length of blooming season for
grapes was twenty days, nineteen days in 1912 and 1914 and twenty-two
days in 1913. The first date in the average year of 1912 was June 14,
while for 1914, it was June 7:

TABLE IV.--SHOWING BLOOMING TIME OF GRAPES

=====================================================================
VERY MID- VERY
EARLY EARLY SEASON LATE LATE
-------------------+---------+---------+---------+---------+---------
Agawam *
America *
August Giant *
Bacchus *
Barry *
Beacon *
Bell *
Berckmans *
Black Eagle *
Brighton *
Brilliant *
Brown *
Campbell Early *
Canada *
Canandaigua *
Carman *
Catawba *
Champion *
Chautauqua *
Clevener *
Clinton *
Colerain *
Columbian Imperial *
Concord *
Cottage *
Creveling *
Croton *
Delago *
Delaware *
Diamond *
Diana *
Downing *
Dracut Amber *
Dutchess *
Early Victor *
Eaton *
Eclipse *
Eldorado *
Elvira *
Empire State *
Etta *
Eumedel *
Eumelan *
Faith *
Fern Munson *
Gaertner *
Geneva *
Goethe *
Gold Coin *
Grein Golden *
Hartford *
Headlight *
Helen Keller *
Herbert *
Hercules *
Hicks *
Hidalgo *
Hosford *
Iona *
Isabella *
Janesville *
Jefferson *
Jessica *
Jewel *
Kensington *
King *
Lady Washington *
Lindley *
Lucile *
Lutie *
McPike *
Manito *
Martha *
Massasoit *
Maxatawney *
Merrimac *
Mills *
Missouri Riesling *
Montefiore *
Moore Early *
Moyer *
Nectar *
Niagara *
Noah *
Northern Muscadine *
Norton *
Oporto *
Ozark *
Peabody *
Perfection *
Perkins *
Pierce *
Pocklington *
Poughkeepsie *
Prentiss *
Rebecca *
Regal *
Requa *
Rochester *
Rommel *
Salem *
Secretary *
Senasqua *
Stark-Star *
Triumph *
Ulster *
Vergennes *
Winchell *
Worden *
Wyoming *
=====================================================================

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