What are preflowers?
Preflowers, as opposed to full blown flowers, generally appear after the fourth week of vegetative growth from seed. Check carefully above the fourth node. Please note that preflowers are very small and and almost impossible to differentiate without magnification. A photographer's 10x loupe is handy indeed when examining preflowers.
As the images below demonstrate, the female preflower is pear shaped and produces a pair of pistils. Frequently, the female preflowers do not show pistils until well after the preflowers have emerged. Thus, don't yank a plant because it has no pistils. Pistillate preflowers are located at the node between the stipule and emerging branch.
Also, some female preflowers never produce pistils. A female preflower without pistils is difficult to distinguish from a male preflower. Thus, hermaphodite issues should not be resolved by the appearance of preflowers, without pistils, on a plant otherwise believed to be a female.
Image courtesy of MrIto
Image courtesy of Uncle Ben
The male preflower may be described as a "ball on a stick." However, its most recognizable feature is its absence of pistils. Sometimes, a male plant will develop mature staminate flowers after prolonged periods of vegetative growth. These appear in clusters around the nodes.
The following image shows a male plant in early flowering. Staminate flowers are located at the node between the stipule and emerging branch.
Image courtesy of PLAYn
Image courtesy of PsycoXul