The juice vesicles (or pulp) of a citrus fruit are the membranous content of the fruit’s endocarp. The vesicles contain the juice of the fruit. The pulp is usually removed from the juice by filtering it out. The juiciness of the pulp depends on the species, variety, season, and even the tree on which it grew.
Pulp cells often have thin membranes, and they are less regular in shape than other plant cells. They are also very large and protect the seeds of the fruit. The color of the pulp is variable, depending on the species and the ripening stage. Usually, it has the color of the outer peel (exocarp).
About 5% of the weight of an average orange is made up of the membranes of the juice vesicles. 
- Tisserat, Brent; Daniel Jones and Paul D. Galletta (March 1990). "Juice Vesicle Populations in Citrus Fruit". Botanical Gazette 151 (1): 9. doi:10.1086/337806. JSTOR 2995282.
- R. P. Bates, J. R. Morris, P. G. Crandall. "Principles and Practices of Small- and Medium-scale Fruit Juice Processing". Food & Agriculture Org. Retrieved April 13, 2014.