You will recognize them by their fruit. Grapes are not gathered ¹  from thorns or figs from thistles, are they? ² 

Can a fig tree produce olives, my brothers and sisters, ¹  or a vine produce figs? Neither can a salt water spring produce fresh water.

for each tree is known ¹  by its own fruit. For figs are not gathered ²  from thorns, nor are grapes picked ³  from brambles. ⁴ 

After noticing in the distance a fig tree with leaves, he went to see if he could find any fruit ¹  on it. When he came to it he found nothing but leaves, for it was not the season for figs.