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 vari ties 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 *

=====================================================================