Joe, I'll try to explain it in my own words. I'll probably leave out a step or two but others can add into this as it is just for starters on the topic. Here goes: In an ideal pollination situation, the pollen grains lodge on the stigma usually aided and held there by the presence of a liquid called stigmatic fluid . The stigmatic fluid then promotes the formation of a pollen tube on each grain of pollen ( a process called pollen germination). The pollen tubes enter through the stigma and grow down the style close to the ovary where the male genes are released in packets of little tubes, one for each grain of pollen, for example.
But when the entry pathways on the stigma are too small or the pollen tubes are too large to enter or the style is simply too long a travel, cut style or in-vitro methods are often used. The pollen must be germinated first with a sucrose solution to form those little pollen tubes.
As far as temperature goes, I've always found that warm mornings after very warm nights are best for pollination.
