Q.Refer to the given figure and select the correct statement
C
B
A
i. A, B, and C are histogen of shoot apex
ii. A Gives rise to medullary rays.
iii. B Gives rise to cortex
iv. C Gives rise to epidermis
a. i and ii only
b. ii and iii only
c. i and iii only
d. iii and iv only
Step 1. Identify the three layers. The figure shows three concentric zones below the surface of the shoot apex dome — A (outermost), B (middle) and C (innermost). According to Hanstein's Histogen theory, the shoot apex is organised into exactly three such histogens, so statement (i) — 'A, B and C are histogen of shoot apex' — is correct.
Step 2. Trace the fate of A (dermatogen). The outermost histogen, dermatogen, is a single layer that differentiates into the epidermis of the stem, not the medullary rays. So statement (ii) — 'A gives rise to medullary rays' — is incorrect.
Step 3. Trace the fate of B (periblem). The middle histogen, periblem, gives rise to the cortex lying between the epidermis and the vascular cylinder. So statement (iii) — 'B gives rise to cortex' — is correct.
Step 4. Trace the fate of C (plerome). The innermost histogen, plerome, gives rise to the central cylinder (stele) — the vascular tissue, pith and medullary rays — not the epidermis. So statement (iv) — 'C gives rise to epidermis' — is incorrect.
Step 5. Combine the results. Only statements (i) and (iii) are correct; (ii) and (iv) are both false.
(c) i and iii only — A, B, C are the three histogens (dermatogen, periblem, plerome); B (periblem) gives rise to the cortex, while A (dermatogen) actually forms the epidermis and C (plerome) forms the central cylinder (which produces the medullary rays), so statements (ii) and (iv) are wrong.
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