A style guide is a document of text and reference illustrations used to guide artists who work on a Magic set. Anthony Waters, Dan Scott, Greg Staples, Jim Nelson, Kev Walker, Martina Pilcerova, Matt Cavotta, Matt Wilson, and Tomas Giorello all worked as concept illustrators for Dissension.
The Simic center of power is Novijen, Heart of Progress, a bizarre architectural womb that serves as the Simic Combine's scientific campus. As you can see above, the look of Simic architecture is, of course, organic. How does life solve problems? By adapting, fusing, metastasizing, distending, evolving. To create a living space, the Simic evolve a specialized set of organisms that can serve as bricks, mortar, supports, and other infrastructure.
…Which brings us to cytoplasts. As Matt Cavotta discussed during Dissension previews, cytoplasts are globs of tissue that provide a bio-magical conduit of genetic information to and from the host organism. Cytoplasts show up in the style guide only briefly but are everywhere in card art. Specifically they're a visual cue for the graft mechanic – see the aqua-blue blobs attached to the graft critters depicted on Helium Squirter, Simic Basilisk, Sporeback Troll, and Vigean Hydropon. If you see a cytoplast, you're seeing Simic ideals applied in the real world – at least, in Momir Vig's gooey, pulsating vision of the real world.
The other stylistic cues in Simic technology vary between the shaggy-with-moss and ropy-with-vines look of Leafdrake Roost or Vigean Intuition, to the bulbous and translucent look of Protean Hulk or Plaxmanta, to the severe and prosthetic-intensive look of Simic Guildmage or Simic Initiate. The recurring thread here is the well-intentioned augmentation of life for the sake of improvement – evolving inevitably into a runaway evolution for evolution's sake. Is that nature turned into something strictly unnatural? Momir Vig would call it progress!