Richardson: Wheat Breeding 



135 



which a grain of wheat may dcvelo]). 

 The flower itself consists of two parts — 



(a) the protective parts, consisting 

 of glumes and pales. 



(6) the essential parts — the stamens 

 and pistil — i. e., male and female 

 organs. (Fig. 1.) 



We are concerned here especially 

 with the essential organs. The stamens 

 (St.) are three in number, and represent 

 the male organs. Each stamen consists 

 of a slender stalk — the filament, bearing 

 at its summit the anther or pollen sacs, 

 which in the case of the wheat plant 

 consists of four longitudinal chambers 

 containing large numbers of minute 

 pollen grains (sperm cells). 



The female portion of the flower — the 

 pistil — consists of the ovary with a 

 minute ovule (or egg cell). The upper 

 part of the ovary bifurcates and forms 

 two long, slender, feathery structures — 

 the styles. (Fig. 14.) 



The pollen grain falls on the stigma 

 of the flower and "germinates," sending 

 a slender tube through the style until it 

 reaches the ovule when the pollen nu- 

 cleus slips down the tube to join the 

 ovule nucleus, and fusion and fertiliza- 

 tion take place. 



How the crossing is done. — In the case 

 of the wheat plant the flowers are 

 normally self -fertilized. Natural cross 

 fertilization is very rare. Moreover the 

 flowers are hermaphrodite, i. e., male 

 and female elements are borne on the 

 same flower. The wheat plant is said 

 to be in "flower" when the anthers 

 begin to extrude from the glumes. 

 With wheat, however, fertilization takes 

 place before "flowering." In order to 

 cross one variety with another it is 

 necessary that the pollen of one variety 

 should be dusted on the ripe stigma or 

 female part of the second variety. The 

 plant from which the pollen is taken is 

 generally described as the male parent, 

 whilst the plant on which the crossing 

 is done is referred to as the female par- 

 ent. I find the following method gives 

 satisfaction. A well developed "ear" 

 of the "female parent" is chosen and 

 prepared in the following manner : — 



The basal spikelets amounting to approxi- 

 mately one-third of the ear are stripped off, 

 and the top third of the head removed with a 

 pair of scissors. Four or five spikelets are thus 



left on eacli side of the center of the ear. 

 These spikelets invarialjly contain three to 

 five flowers. All flowers save the outside pair 

 are removed with a pair of forceps. Thus the 

 ear is reduced to 12 to 20 flowers (Fig. 18). It 

 is now necessary to "castrate"' the flowers by 

 removing the three anthers from each. The 

 point of the forceps is gently inserted between 

 the upper margins of the inner and outer pales, 

 and, by releasing the pressure on the forceps the 

 flower is gently forced open, exposing the three 

 anthers and the feathery stigma. With a 

 little practice these anthers may be removed 

 unbroken with one stroke of the forceps. It is, 

 of course, necessary to prepare the ear in this 

 fashion before any of the anthers have shed 

 their pollen grains. The best stage at which to 

 carry out the operation is when the anthers are 

 just approaching maturity and turning yellow 

 in color. Having castrated the whole of the 

 flowers by the removal of all traces of the 

 anthers, the ears may be wrapped in cotton 

 wool until the stigmas of the flower become 

 "receptive" or ready to receive the pollen. 

 The cotton wool may then be removed, and 

 ripe anthers of the particular variety desired 

 as the male parent should then be secured. 

 The anthers should be quite "ripe,"^. e., bright 

 yellow in color, and just ready to burst. The 

 anthers are seized with a fine pair of forceps, 

 broken in halves, and the contents gently 

 shaken or dusted over the feathery style of the 

 female ear. Each flower is treated in succession 

 in this way, and frequently, when the pollen is 

 not in good condition, some of the anthers may 

 be broken and left inside the protective glumes 

 of the flower. 



Instead of castrating and pollinating flowers 

 on different days it is generally more convenient 

 to remove the anthers and cross-pollinate the 

 stigmas at the one operation. It is necessary 

 in such cases that the stigma and anthers 

 should be fairly "ripe," and care should be 

 taken that self-fertilization does not occur. 

 Any flowers in which the antherS have already 

 liberated pollen should be suppressed. 



After the crossing is finishe'd the ear is 

 wrapped up in cotton wool, or surrounded with 

 a light paraffined paper bag to prevent the 

 possible entry of foreign pollen. The ear is 

 then labelled with the names of the male and 

 female parents, date of cross, etc., and sup- 

 ported by a stake. A fortnight later' the 

 protective covering may be removed, and the 

 ear allowed to ripen. 



EFFECTS OF CROSSING. 



It is interesting to note, in passing, 

 the general effect of crossing two 

 different varieties of wheat : — 



(a) Crossing Increases Vigor of Prog- 

 eny. — Darwin made an exhaustive 

 comparative study of the effects of 

 self-fertilization and cross-fertilization 

 in plants. He has strmmed up hi? 

 researches in the generalization that 

 "Nature abhors perpetual self-fertiliza- 



