Pumpkin Stem Cross Section

 When fall arrives and the air smells crisp and fresh, pumpkins are on every botanist's and gardener's mind. Pumpkin stems are examples of  classic dicot stem arrangement with a few slight differences. The first indicator is the circular arrangement of the vascular bundles. However, due to the pumpkin's  size, the five vascular bundles in pumpkin stems are larger than in other plants. 

The large circles are the xylem. The xylem consists of cells that are dead at functional maturity, and it transports water and minerals from the root system to the rest of the plant. The small circles on the upper left are the phloem, which consists of living cells that distribute the products of photosynthesis. 

As seen here, the epidermis is quite thick compared to other plants

Indicated by the gap through the middle, the central pith is not present, having disintegrated early in the development of the stem.

Objective: 4x (previous 5 photos)

Objective: 10x (previous 4 photos)

These purple molecules appear to be serpins, but I am not fully certain. Important to plant defense, serpins are present in phloem sap and irreversibly inhibit the digestive proteases from pests or pathogens.

More information regarding serpins is available here: https://www.researchgate.net/publication/230734040_Plant_Serpins

Objective: 40x (previous 3 photos)