In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: These data suggest that 1 ) apigenin delays the long - term forgetting but did not modulate the 24 h retention of fear memory and 2 ) the obtained beneficial effect of apigenin on the passive avoidance conditioning is mediated by mechanisms that do not implicate its action on the muscarinic cholinergic system .
### Output Text:
These data suggest that 1 ) <span class="chemical">apigenin</span> delays the long - term forgetting but did not modulate the 24 h retention of fear memory and 2 ) the obtained beneficial effect of <span class="chemical">apigenin</span> on the passive avoidance conditioning is mediated by mechanisms that do not implicate its action on the muscarinic cholinergic system . 