Explain.

Dear student,
 ​Kindly mention the statement which is not clear to you. I am explaining in brief all the statements mentioned.

• All secondary meristems are lateral meristems because they cause lateral growth by covering the stems and helping in lateral growth i.e. increase in thickness of stems.
• Lateral meristems are generally cylindrical because they surround the stem of plants, therefore they are cylindrical.
• Primary meristems helps in the primary growth of the plants root or shoot therefore they appear earlier than secondary meristems (which increases the thickness of the roots or shoots).
• Apical meristems are present at the shoot or root tips and helps to increase the length of the root or shoot because the cells of apical meristems can only increase the length of plant parts. In most algae and fungi all the cells are divisible so the growth occurs in all direction and shows diffused growth.
• In brown algae, bryophytes and lower pteridophytes, apical meristem contains single cell. Therefore it is called apical cell which is pyramidal in shape.
• In developed plants like ferns, gymnosperm and angiosperm apical meristem contains many cells. 

Regards