One of the highlights thus far of the 2006 gallery season has been Tara Donovan’s “Untitled (Plastic Cups),” an unforgettable installation that filled PaceWildenstein’s 22nd Street space in March and April. This brilliantly original work used nearly 3 million plastic cups to fashion a sprawling landscape of jagged hills and deep craters. As challenging as it was spectacular, the piece also presented a series of conceptual tensions — between its mundane material and its magisterial grandeur, between the suggestion of recognizable form and the bare fact of its total abstraction — that gave it the imposing mental resonance characteristic of all first-rate achievements.

“Tara Donovan: Rubber Band Drawings,”the artist’s follow-up, is a decidedly quieter affair. But if none of the 11 untitled works (2005–06) gathered at Pace’s 25th Street space achieves the jaw-dropping splendor of “Untitled (Plastic Cups), “they collectively remind us of Ms. Donovan’s uncanny ability to use an everyday industrial product to create wonderfully intricate abstract forms.

Technically speaking, none of these images is actually a drawing.To make them, Ms. Donovan fastened hundreds, in some cases thousands, of rubber bands to a rectangular board to create densely patterned geometric designs. Each board was inked and then pressed like a stamp onto a 53-inch-by-42-inch piece of Kozo-shi paper.

The results are wonderfully ornate patterns. In one, hundreds of tautly stretched rubber bands converge on a central point from all directions, evoking a shaggy head of hair or an army of sperm attacking a lonely egg. A second image presents a floral pattern with delicate but pointed leaves. Elsewhere are designs that suggest a spiraling black hole, a mass of protozoa swirling around a petri dish, a loose mosaic of circular stones, droplets of water streaking a window, and the flowing strands of a feather.

Two pieces have graceful, gently lilting lines that recall Al Hirschfeld drawings. But whereas Hirschfeld’s curves coalesced into impressions of swollencheeked singers, leg-thrusting dancers, or wry, ironizing actors, Ms. Donovan’s never come together, each remaining an isolated squiggle.

The creative exercise that these drawings represent can seem similarly incomplete. Ms. Donovan has created 11 rather beautiful and surprising works, yet something is missing, especially when one thinks of her plastic cup installation.The problem may very well be the absence of the rubber bands themse lves. These demure, subtle images would certainly benefit from a bit more of the sticky-stretchysquishy qualities of the bands of rubber that made them possible. Unfortunately, the immensely inventive Ms. Donovan has not fully exploited the essential playfulness of her material.

***

Tomas Saraceno’s “Air-Port-City,” on display at the Tanya Bonakdar Gallery, is a wide-eyed speculative fantasy of an exhibition. The artist’s five works are part of an ongoing exploration of the possibility of creating human habitation that is airborne rather than earthbound.

His two “Flying Gardens” (both 2006) borrow forms from the geodesic dome of Buckminster Fuller, whose eco-utopianism clearly influenced this body of work, and they riff on the fanciful idea of a floating, sustainable ecosystem. “Cumulus” (2006) is a two-minute loop of still photographs taken at Salar de Uyuni, Bolivia, the world’s largest salt lake, whose mixture of pale blue and white coloring looks like a cloudy sky.

“Mars on Water” (2005) is an apparently understated installation consisting only of a piece of white paper and a glass of water.Yet if you dip your finger in the water and let a drop fall onto the page below, you will discover that the liquid does not dissolve but is instead enclosed in a transparent bubble that looks like a plastic pebble. The paper, it turns out, is coated in Aerogel, a spongelike insulating substance that NASA used in its Stardust mission to trap interstellar dust particles. Reversing the usual question about whether there is water on Mars, this work suggests a way to transport the life-bearing compound to the most inhospitable corners of the universe.

The final piece in the show, “Ladies and Gentlemen We Are Flying in Space” (2003/06), is a desktop installation comprising a stapler, a lamp, and a piece of string with a screw at its tip that rises, in a seemingly gravity-defying act, from the base of the stapler to a centimeter or so from the rim of the lamp. The menacing gesture of the screw reads as an act of naked aggression — a cruising missile frozen in the moment before impact — but upon closer inspection the work transforms into an example of symbiotic equilibrium: The screw and the taut string attached to it are held in place by a thick magnet fastened to the inner lip of the lamp head.

“Ladies and Gentlemen,” like all of Mr. Saraceno’s works, asks its audience to look beyond the expected and to imagine what happens when human imagination and scientific know-how work together. His hopeful project also manages to bridge the gap between faith and science — no small achievement in this polarized moment, when the only choices often seem uncompromising atheism or reactionary religiosity.

As a whole, the artist’s creations lack the aesthetic appeal of Ms. Donovan’s rubber band drawings and thus can seem inadequate containers for such buoyant utopian musings. But this criticism could probably be thrown at all grand visions in their earliest stages. Whatever its limitations, Mr. Saraceno’s work is an invitation to accompany the artist on a crazy dream, an ecologically compelling, romantic fantasy of the high life that looks like quite a trip.

Donovan until August 26 (534 W. 25th St., between Tenth and Eleventh avenues, 212-929-7000). Saraceno until August 4 (521 W. 21st St., between Tenth and Eleventh avenues, 212-414-4144).