Final answer:
The diagram shows geotropism. The guidelines in the diagram need to be labeled with specific details. Light and water can be effective stimulants for part 2, and mosses and ferns may grow towards the gametophyte with the help of these stimulants.
Step-by-step explanation:
a) The type of tropism shown in the diagram is called geotropism or gravitropism. Geotropism is the growth or movement of an organism in response to gravity.
b) The guidelines labeled 1 to 4 indicate the steps to observe and analyze the tropism. Specific details about the diagram would be needed to provide accurate labels.
c) Two effective stimulants that help in the growth of part 2 could be light and water.
d) Two groups of plants where part 2 grows towards the gametophyte with the help of the stimulants mentioned in C could be mosses and ferns.
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