In $Ginkgo$,the male gametes are ...... .

The secondary wood of $Pinus$ is characterised by:

Gymnosperms lack .......... .

$A$ transverse section of a plant organ shows vessels but does not show companion cells. This organ may belong to:

Select one of the following pairs of important features distinguishing $Gnetum$ from $Cycas$ and $Pinus$ and showing affinities with angiosperms.

Vessels are absent in