*Observation*


( ) <sup>=</sup> <sup>×</sup> Total number of dividing cells Active Mitotic Index % <sup>100</sup> Total number of cells observe *AMI*

*Pollination Biology and Environmental Water Pollution Indicator of Onion (*Allium cepa *L.) DOI: http://dx.doi.org/10.5772/intechopen.111475*

• *Total Abnormality Percentage (TAP) %* was computed using following formulae:

( ) <sup>=</sup> <sup>×</sup> Number of abnormal cells Total Abnormality Percentage % <sup>100</sup> Total number of cells scored *TAP*

#### **2.8 Statistical analysis**

The experiments were conducted according to randomised complete block design (RCBD) with three replications. Data were expressed as mean ± standard error (SEM) [14].

### **3. Result**

#### **3.1 Phenological and growth variable**

The onion (*A. cepa* L.) is a biennial crop that completes the life cycle in 2 years i.e., 1 year after plantation, using the nutrients from the soil, we get the onion bulb which is the vegetable. Second year that particular size of vegetable bulbs is used for the production of fleshy peduncles and seeds. In the study after sowing the onion bulbs the peduncle started flowering within 45.03 ± 0.98 days (**Figure 1b** and **Table 2**). The flowers are raised on the top of single very compressed hollow internode as a peduncle. Each plant contained around 4.25 ± 1.00 number of peduncles with many other chlorophyll less fleshy leaves and each hollow peduncle length was about 68.45 ± 0.58 cm. Each peduncle held on the top of an umbel inflorescence consisted of 306.78 ± 29.0 florets (**Figure 1f**). Initially, small size inflorescence of *A. cepa* L. covered by 2 layers of white colour membrane called spathe. These spathes protect the juvenile buds of the umbel inflorescence. Due to the increase in the internal pressure of the florets, the spathe splits open which took 8–10 days. It was noticed that around 6 O'clock early in the morning anthesis takes place but the temperature is the crucial factor for the initiation of the anthesis. Fertility of the pollen along with stigma receptivity was observed the highest on the day of anthesis. In two whorls arrangement hold both the perianth and six number stamens. The stamen was found to be 0.71 ± 0.19 cm in length and consists of a bilocular anther 0.22 ± 0.10 cm long (**Figure 1j**). The anther splits longitudinally to release the pollen grains and takes the entire day for its dehiscence. Pistil length (with superior ovary) was 4.50 ± 0.58 mm (**Figure 1i**, **j**). In the normal condition, only one pedicel was carried by a single floret but in this experiment, it was observed that there were two florets attached to the single pedicel (**Figure 1g**, **h**). Different species of the genus *Allium* show the variable colour combination among the inflorescences (**Figure 1c**). The onion flower releases a very strong odour which attracts various insects for cross-pollination. The presence of nectar in flowering plants attracts insects which makes interspecific relationship for cross-pollination in the plants for hybrid vigour seeds production. Morphologically bowl-shaped florets of the onion inflorescence produce nectar with hidden nectarines (**Figure 1o**, **p**) thus act as a good food reward and attract a wide range of vectors among which few of them are pollinators. These vectors belong to different families. One of the family Apidae including honey bees such as *Apis cerana* and *Apis florea* were found in the field most of the time (**Figure 1l**). Another insect was noticed with elongated siphon which might help to suck the nectar from inside of the floret

(**Figure 1 k**, **m**, **n**). Very good relationships between pollinators and temperature were observed as the pollinator movement was maximum in first half of the day and slowly decreased when temperature increased.
