In　this　paper,　we　consider　a　modified　delay　differential　equation　model　of　the　growth　of　n-species　of　plankton　having　competitive　and　allelopathic　effects　on　each　other.　We　first　obtain　the　sufficient　conditions　which　guarantee　the　permanence　of　the　system.　As　a　corollary,　for　periodic　case,　we　obtain　a　set　of　delay-dependent　condition　which　ensures　the　existence　of　at　least　one　positive　periodic　solution　of　the　system.　After　that,　by　means　of　a　suitable　Lyapunov　functional,　sufficient　conditions　are　derived　for　the　global　attractivity　of　the　system.　For　the　two-dimensional　case,　under　some　suitable　assumptions,　we　prove　that　one　of　the　components　will　be　driven　to　extinction　while　the　other　will　stabilize　at　a　certain　solution　of　a　logistic　equation.　Examples　show　the　feasibility　of　the　main　results.　(C)　2006　Elsevier　B.V.　All　rights　reserved.