The Collaborative International Dictionary of English v.0.48:

Pullulate \Pul"lu*late\, v. i. [L. pullulatus, p. p. of
   pullulare to sprout, from pullulus a young animal, a sprout,
   dim. of pullus. See pullet.]
   To germinate; to bud; to multiply abundantly. --Warburton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pullulate
    v 1: be teeming, be abuzz; "The garden was swarming with bees";
         "The plaza is teeming with undercover policemen"; "her mind
         pullulated with worries" [syn: teem, pullulate,
         swarm]
    2: move in large numbers; "people were pouring out of the
       theater"; "beggars pullulated in the plaza" [syn: pour,
       swarm, stream, teem, pullulate]
    3: produce buds, branches, or germinate; "the potatoes sprouted"
       [syn: shoot, spud, germinate, pullulate, bourgeon,
       burgeon forth, sprout]
    4: become abundant; increase rapidly
    5: breed freely and abundantly

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "pullulate":
   abound, abound with, be alive with, be fruitful, be productive,
   beget, blossom, brew, bristle with, bud, burgeon, burst forth,
   burst with, clutter, crawl, crawl with, creep with, crowd, develop,
   engender, fill, flood, flourish, flow, fructify, gather, gemmate,
   germinate, grow, grow rank, grow up, hypertrophy, increase, jam,
   know no bounds, leaf, leaf out, leave, luxuriate, mature, multiply,
   mushroom, outgrow, overabound, overbrim, overdevelop, overflow,
   overflow with, overgrow, overrun, overspill, overspread, overswarm,
   overtop, pack, procreate, proliferate, pullulate with, put forth,
   put forth leaves, put out buds, reproduce, riot, root, run riot,
   shoot, shoot up, spill over, spring up, sprout, sprout up,
   strike root, superabound, swarm, swarm with, take root, teem,
   teem with, thrive, throng with, tower, upshoot, upspear, upspring,
   upsprout, vegetate, wax