I'd better correct my fuzzy explanation above before I confuse anyone else (or myself) further.
My assessment of what Minor White was doing above was a bit unclear. He is obviously placing his shaded palm in Zone VI. This is, as Bill points out, similar to taking an incident reading in the shadow and closing two stops. White seems to have used this method to hold good shadow detail in the shaded areas. The rendering of subjects in the shadows are two-stops "underexposed" as compared to a "correct" exposure for subjects in that light alone, which ensures that middle gray shaded subjects end up in Zone III, i.e., as detailed blacks. A pretty safe shadow placement.
This results in a lit reading of his palm ending up in Zone VI (the "correct" Zone) only if there is only a two-stop difference between the illumination in lit and shaded areas. This is common, but in many outdoor scenes the difference in illumination between lit areas and open shade is greater than this, sometimes three or even four stops.
Variations of the "Sunny-16 Rule" recommend opening up from two to four stops for subjects in open shade (one reason I like to use a meter... there seems to be some questions about what common outdoor lighting ratios are). White's placed palm would fall in Zone VIII if the lit area were 4 stops brighter than the shaded area, or in Zone VII if the difference were three stops. This would result in overexposure of the lit subjects unless development was appropriately reduced from "Normal." I assume White took some readings of the lit area and adjusted his development accordingly as well.
In a situation where the lighting difference between shaded and lit areas is four stops (incident reading), opening two stops from the lit reading, or closing two stops from a reading taken in the light will result in the same exposure.
On a bright sunny day, with important subjects both lit and shaded, taking a reading of the lit area, or an incident reading of the light, or a palm reading in the light will usually result in underexposure, unless the shadows are pretty bright. I've heard the admonition to open up a couple of stops from such a reading in a bright contrasty situation (and reduce development accordingly), which is the source of my mistake a few posts earlier.
At any rate, I use spot-metering techniques for almost everything anymore, and haven't used an incident meter in years.
I'll quit now... I'm not helping the OP anymore.