With the exception of Chevrolet, American entry-level automobile brands usually didn't retain grille design themes for very long (for instance, I dealt with Ford's short-lived spinner theme here).
So it was with Plymouth during the era of American car sporting grilles comprised of thick, chromed bars assembled into bold compositions.
From 1946 through 1948, Plymouth styling was static because this was the period of the post - World War 2 seller's market. The grille was essentially a set of V'd horizontal chromed strips with areas of painted body metal and openings between them.
The entire Chrysler Corporation line was completely restyled for the 1949 model year. Plymouth's grille retained the horizontal chromed-bars theme, though a vertical bar was added at the center. Missing are the bits of body metal.
The thinner grille bars were deleted for 1950, resulting in a "gunsight" composition that Dodge has since used for many years.
This is from the time when advertising artists were told to distort the shapes of cars to make them appear longer, lower, sleeker. Actual 1951 Plymouths had the same tall, boxy body as seen in the previous photo; the main difference was that the nose of the hood was rounded down. That said, this illustration clearly shows the grille elements. Three bars are retained, but the upper two are curved down towards their edges. Added are three widely spaced vertical "teeth" that were in keeping with the American fashion of bold grilles. The 1951 grille was unchanged for the 1952 model year.
Chrylser brands were redesigned for 1953. The Plymouth grille is essentially a single bar along with a chromed frame for the upper edge of the air intake. The center third of the bar is chromed, while the surrounding segments are painted body-color. Nine small chromed half-bangles are distributed across the length of the bar. Altogether, a considerable change from the previous year.
A photo I took at the LeMay museum in Tacoma. Gone are those curious little wrap-around vertical chromed accents. The large bar is still divided into three segments, but horizontal chromed overlays were added that wrap around to become parts of the side trim. A smaller, all-chromed horizontal bar had been placed below the main bar. Sales of all Chrysler Corporation marques were falling and stylists were desperately trying to help tide things over until the redesigned 1955 line was announced. Perhaps this explains why the elements in the central part of the grille are chaotically themeless.
Chrysler Corporation brands came roaring back, sales-wise for 1955, along with most of the rest of the U.S. automobile industry. The Plymouth line was tastefully styled, including the grille which was still in the American idiom of bold chromed bars. We see that Plymouth returned to the 1953 recipe of one large horizontal bar along with an upper accent bar. The three-element aspect is also retained, though I doubt that most people ever noticed this (I didn't until I was writing these words). The bends of the bar and faux-teeth add interest and strike me as being more in keeping with the notion of the automobile than the tacked-on treatment of 1953.