We assume that she grew the paperwhite narcissus over water and not in soil. Unless the water is so salty, alkaline, or acidic that the developing roots are damaged, bulbs are not very fussy about the quality of water.
The qualities that most determine the growth of a bulb are its size and health. Bulbs naturally come "packaged" with all the nutrients they need to grow and flower. Therefore, distilled water should work as well as melted snow or rainwater provided that the bulbs are all healthy and of the same size and are grown under identical conditions (amount of light and temperature).
Adequate light, proper temperatures, and sufficient moisture are external variables that should be controlled in the experiment. Damage can occur to bulbs during handling or storage. Exposure to very warm or freezing temperatures or ethylene gas can keep bulbs from growing or blooming normally.
True bulbs such as paperwhite narcissus are made up of many swollen leaf bases growing close together below the surface of the soil, and they store carbohydrates (sugars and starches) in these leaf scales. The roots originate from the flattened base of the bulb which is called the basal plate. Inside the bulb is a small preformed flower called the primordium which will mature and bloom unless the bulb is damaged.
It would be interesting for your daughter to dissect one of the bulbs and draw what she sees inside. (To cut bulbs in half, slice lengthwise, from the pointed top down through the base of the bulb.)
Did your daughter carefully examine and weigh each bulb before the experiment? The size of the bulb is directly related to the amount of stored carbohydrates and thus the ultimate size of the plant and flower. The best bulbs are the largest and plumpest. (Avoid shriveled or moldy bulbs.)
Other important aspects of your daughter's experiment would be to compare:
- the end results of growing with the different water sources,
- the size of the blooms,
- the weight of the entire plant, and
- the height.
