Garlic is a shallow-rooted crop, which has no root. Hair roots are located around the shortened stems, with the most on the outside and less on the inside (Figure 1). The root system is string-shaped, with few root hairs and weak absorption. It is distributed in the plough layer of 5 ~ 25 cm, with a transverse diameter of about 30 cm, showing the characteristics of being wet and fat-loving. Before sowing, the root protrusion has formed at the base of garlic cloves, and the rooting position is mainly at the edge of the stem disc on the back of the seed cloves, and the amount of roots on the ventral surface is very small. According to the observation of Zhang Shaowen et al. (1986), under the condition of autumn sowing in Henan Province, garlic has two rooting peaks in its life, the first peak is 1 week after sowing, and the original root primordia are rapidly extended under suitable conditions, forming young new roots15 ~ 40. The second rooting peak began in April, when the stem and leaf were in the peak growth period and the garlic bolt and garlic clove were differentiated and formed. At this time, a large number of new roots laid the foundation for the expansion of bulbs and the elongation of garlic bolts. With the growth of the plant and the enlargement of the stem disk, the root system gradually moves up, and it shows the replacement of new and old roots. In mid-May, the high temperature came, which caused the root system to age and start to die.

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Figure 1 Morphological diagram of garlic organs

1. fibrous root 2. stem disk 3. bulb 4. leaf sheath 5. flower bud 6. bud hole

The stem disk is disk-shaped, the internodes are very short, and the growing points are covered by leaf sheaths. With the growth of the plant, the height of the adult stem is about 1 cm and the transverse diameter is 2 cm. After flower bud differentiation, flower buds (garlic shoots) are drawn from the top of stem plate, and the top of flower buds is an involucre, in which the original body of flowers and aerial bulbs are differentiated, and flowers and aerial bulbs are arranged alternately, so the differentiation of flowers is later than that of aerial bulbs, and flowers can not form seeds when degenerated. Some plants form aerial bulbs, which have no essential difference in structure from bulbs and can be used as sowing materials. However, due to the small size, garlic usually grows into a single-headed garlic in the year of sowing, and then it can be sown with a single-headed garlic to form a split garlic.

Garlic leaves include leaf body and leaf sheath. Garlic leaves are flat, narrow and long, banded, dark green, upright, waxy on the surface, and have the characteristics of drought tolerance. According to Cheng Zhihui's research (1997), the average leaf length and width of different garlic varieties are (40.8 6.2) cm, (2.73 0.53) cm, and the leaf shape index is15.12.2. The leaves of high latitude varieties are narrow, short and straight; The leaves of middle and low latitude varieties are wide, long, soft and drooping. Before sowing, 5 young leaves have been differentiated in the seed petal, and after sowing, new leaves will continue to differentiate; After flower bud differentiation, the differentiation of new leaves stopped and the number of leaves no longer increased. Garlic leaves alternate and are symmetrically arranged, and the direction of the leaves is perpendicular to the connecting line between the dorsal and ventral parts of garlic petals. When sowing, if the connecting line between the dorsal and ventral parts of garlic petals is parallel to the row direction, the leaves can receive more sunlight.

The leaf sheath is tubular, and the leaf body is folded before exhibition. After exhibition, it is flat and long, with parallel veins and alternate leaves, with a 1/2 leaf sequence, symmetrical arrangement and spreading degree of 35 ~ 45 cm. Leaf sheaths are nested with each other to form pseudostems, which have the functions of support and nutrient transportation. Generally, the height of pseudostems is 30 ~ 50 cm, and the transverse diameter is1.5 ~ 2.5 cm. The leaf body is 55 ~ 65 cm long and 2.5 ~ 4 cm wide. The later the leaf differentiation, the longer the leaf sheath; The more leaves there are, the stronger the pseudostem is. In seedling stage, the thickness of pseudostems is similar, and the base of leaf sheath thickens with the expansion of scale buds. At the peak of bulb expansion, the nutrients accumulated at the base of leaf sheath moved inward to the scale bud, which caused the outer leaf sheath to gradually shrink into a film shape and wrap the scale bud, so that garlic could be preserved for a long time.

Cheng Zhihui and others (1990, 1995) first reported the abnormal phenomenon of garlic tubular leaves and its influence on garlic yield and quality. This phenomenon mainly occurs in Cangshan garlic, and the plant rate is as high as 30%. The leaf shape of a tubular leaf plant at a certain position is similar to that of an onion leaf, and each plant can produce1~ 3 tubular leaves. Because the tubular leaves hinder the growth and function of the late differentiated internal leaves, the garlic shoots are thin and short, the garlic heads are small, and the yield is reduced by about 30%.

The number of garlic leaves varies with varieties and sowing dates. Generally, garlic leaves are12 ~15 in autumn and 9 ~13 in spring. The more leaves there are, the larger the leaf area is, and the longer the functional period of leaves lasts, the more favorable it is for the elongation of garlic shoots and the expansion of bulbs. Therefore, the leaf area should be enlarged before bulb formation, and the premature aging of leaves should be prevented during bulb formation. According to the observation of Zhang Shaowen et al. (1986), there are two peaks in the growth of leaf area of autumn sowing garlic. The first peak is before the garlic overwinters, the leaf area per plant can reach 150 cm2; The second peak period is from late April to early May before garlic bolting, and the leaf area per plant can reach 700 ~ 800 cm2. Gu Zhizhang (199 1) reported that the growth of garlic leaf area in seedling stage and garlic bolting stage accounted for 40% of the total leaf area respectively. The newly added leaf area accounts for 20% of the total leaf area during flower bud differentiation. By the middle stage of bulb expansion, the leaf area decreased by 20% due to the gradual aging of leaves, and the leaf area decreased by 50% in the late stage of bulb expansion.

The effect of photosynthetic products of garlic leaves on garlic yield has certain regularity. According to the data, the photosynthetic products of leaves in the lower position of 4 ~ 6 in the early stage are mainly used for vegetative growth; The photosynthetic products of the middle leaves at 7 ~ 9 leaves in the middle stage are mainly used for the growth of garlic bolts, and the input to garlic is higher than that in the early stage. In the late stage, the photosynthetic products of the leaves at the upper position of10 ~12 accounted for nearly 90% of the total input to garlic. Therefore, protecting the green leaves in the later stage of garlic is the key to improve garlic yield.