The Final Riddle!

Dear Journal, The progress with discovering exactly what Ellysian is hiding hasn't been going well. Every time Gieaun, Scede and I try to sneak onto the trail we either get blocked by the twins or their friends, or it is time to go back to class. We decided to give it up for now and to try again after the weekend. For now, I'll have to tell you about something else; Mr. Cohrbin gave us the last riddle today! At least, the last riddle that is somehow connected to the others. He said that next week he'll start giving us different ones. Master Hroombra promised to help me with them in the next few days, so I'm sure to discover what they mean! And can you believe it? No one's figured them out yet, not even the older students! I think Mr. Corhbin is very disappointed in us. Well, here's the riddle, I hope to have it figured out (and the rest of them) by next week: Of the four Sisters I'm the last to show, When the earth seems still and the growth is slow. I'm harsh and bitter and my bite will sting; You'll know I've left when the birds begin to sing. -Jahrra