The recent news that Streit’s matzo factory, on the northeast corner of Rivington and Suffolk streets, is up for sale — and will in all likelihood yield to condominiums — is just the latest in a series of reminders that the Lower East Side is changing dramatically, and losing those last few tokens from its era of mass immigration of Eastern European Jews.

A stroll west on Rivington from Streit’s (which apparently will remain in operation for the time being and can still be visited) shows the old and the new East Side in clearer relief than does a stroll anywhere else in the neighborhood.

Diagonally across Rivington from Streit’s stands the exuberantly gabled Public School 160, built in 1898, one of countless gems by C.B.J. Snyder, who was New York City’s public-school architect in the late 19th and early 20th centuries. Step back to look at the building above its sidewalk scaffolding. Little is known of Snyder’s background, but he was an inventive designer who at his best created school buildings that were appropriately monumental in their neighborhood settings, and that also, in both their massing and their ornamentation, showed a light-handedness that kept the often (as here) gigantic buildings from ever feeling oppressive. Yet that didn’t stop later architects from deciding that the old schools were all wrong for kids, who needed modular floor plans, larger schoolyards, and bigger windows, and who, experts warned, felt discomfited by atavistic ornamentation. Thus compare P.S. 160 to Intermediate School 25, from the 1970s, right across Rivington.

At the southeast corner of Rivington and Norfolk streets, Keith McNally’s restaurant Schiller’s represents the many nouveau eateries throughout the Lower East Side. Turn left on Norfolk. On the west side of the block between Norfolk and Delancey stands architect Bernard Tschumi’s high-rise apartment building named Blue (2006), for the color of the glass façade of this avant-garde heap. Blue’s architect was once the dean of the School of Architecture at Columbia University, and the designer of Parc de la Villette in Paris. The new Lower East Side is being marketed to the well-to-do who get a charge from edgy surroundings, a bit as they did in SoHo or TriBeCa in the 1980s. But whereas large parts of those areas were designated as historic districts by the New York City Landmarks Preservation Commission, none of the Lower East Side has been, making the area ripe for the interventions of hot architects. Truth to tell, Blue’s block of Norfolk doesn’t belong in a historic district. My feeling is that if the city is inevitably going to get chichi buildings of the type we call “object buildings,” that loudly call attention to themselves, we may as well slot them on nondescript blocks such as this one.

For me, the architectural quality of the Lower East Side resides, apart from in its synagogues, in tenement buildings such as the one at the southwest corner of Rivington and Norfolk. Designed by Alfred E. Badt, 129 Rivington St. was built in 1902, one year after the Tenement House Law that brought sweeping, humane reforms to the design of multiplefamily dwellings in New York City. The nicely patterned brickwork and spirited terra-cotta ornamentation in the Beaux-Arts manner, and the sleekly rounded corner bring an immense dignity to this building. I suspect that those who moved into it in 1902 felt a pride that Blue probably can’t quite elicit. (Badt designed 129 Rivington St. right before his distinctive Pike Street Synagogue of 1903–04, on Pike Street at East Broadway.)

Between Essex and Ludlow streets, note Economy Candy Company, at 108 Rivington. It’s one of the neighborhood’s old-time businesses that appears to be still going strong. It was founded in 1937, and has been in the current location for the last 23 years. Right across Rivington is the chic restaurant Thor, embedded in the Hotel on Rivington (the initials of which form the restaurant’s name), a 20-story tower of glassy hipness designed by Matt Grzywinski and Marcel Wanders.

Between Allen and Eldridge streets, the former synagogue built for Congregation Adath Jeshurun of Jassy, on the north side of Rivington, is one of the architectural highlights of the Lower East Side. Erected in 1903, it was designed by Emery Roth at the same time he designed his wonderful Hotel Belleclaire on Broadway at 77th Street. Between the Moorish style of the synagogue and the Art Nouveau of the apartment hotel, you’d never guess that the Hungarian émigré had only recently assisted his mentor Richard Morris Hunt in the design of the grand Beaux-Arts Breakers mansion in Newport, R.I. All three works are as different in style from one another as can be — and such variation was a hallmark of the architect’s career. We seldom see this Moorish synagogue style handled with such vigor and self-assurance. The banded brickwork, the great corniced arch, and the beautiful wheel window richly reward a view.

Across Rivington from the synagogue stands the very large University Settlement house, built in 1898 for the organization founded in 1886 by Stanton Coit, Charles B. Stover, and Carl Schurz. The building’s architects were Isaac Newton Phelps Stokes and John Mead Howells. The former, descended from two of New York’s philanthropic old-money families, had just returned from three years at the École des Beaux-Arts in Paris. Howells was the son of the novelist and critic William Dean Howells. They went on to design the splendid St. Paul’s Chapel at Columbia University; Stokes wrote the six-volume “Iconography of Manhattan Island,” published between 1915 and 1928, the greatest history of New York; and Howells was Raymond Hood’s partner in the competition-winning design of the Tribune Tower in Chicago. Here on Rivington Street, their restrained classicism resulted in a somewhat austere but dignified building, and if a note stands out among Rivington’s older buildings, it is that of dignity.