Epiphytes like Vanda develop special layer of absorptive tissue velamen consiting of $4 $ or  $5$  layers of long polygonal cells. Velamen is formed by

Which of the following pairs of family's posses pollinia?

Approximate diameter of Victoria leaf is

Petiole is modified into tendril in

Which one of the following conditions is seen in the roots of a plant having submerged assimilatory roots and spongy petioles?