## 2 Materials and Methods
### Optical Coherent Tomography (OCT) Experimental System  
A schematic diagram of the spectral-domain optical coherence tomography (SD-OCT) is shown in Figure 1. A superluminescent diode (SUPERIUM, SLD-137-HP3-DBUT-SM-PD, Cork, Ireland) with a central wavelength \(\lambda_{0}\) = 836.1 nm and a bandwidth \(\Delta\)\(\lambda\) = of 55.2 nm, providing a total outpower of 15.6 mW, was used as a light source. The light from the light source was first coupled to the input port of the circulator (AC Photonics, Inc., Santa Clara, CA, USA) and further divided into two beams by a 2 \(\times\) 2 50/50 fiber coupler (TW850R5A2-2 \(\times\) 2 Wideband Fiber Optic Coupler, 850 \(\pm\) 100 nm, THORLABS, Exeter, UK), illuminating the sample seed and the reference mirror, respectively. The reference arm consisted of collimating lens L1, objective lens L4, and mirror M1, and the sample arm consisted of lenses L2, L3 (LSM03-BB--Scan Lens, EFL = 36 mm, THORLABS, Exeter, UK), and Galvano scanning mirrors. Dispersion was compensated by a glass plate placed in front of the reference mirror, followed by offline mathematical compensation following the collection of data. Light from L3 was reflected by mirror M2 to the seed. The power of the light incident on the seed in the sample arm was 2.6 mW, which is below the irradiance damage threshold for seeds. The two-dimensional scanning mirror (Galvano mirror scanners) can scan laterally in the X and Y directions. The sensitivity was measured to be 96 dB at a depth of 0.24 mm. The sensitivity roll-off was around 7.94 dB/mm. Each measurement is a 2048 (x) and 512 (z) raster scan over an area of 3.1 \(\times\) 1.6 mm\({}^{2}\) at an acquisition rate of 10 frames per second (fps). A total of 100 cross-sectional images were recorded. The fiber coupler recombined the backward scattered light from the seed and the reflected light from the reference mirror. This light was directed through a circulator to a spectrometer that consists of a collimator, lens L5, and a grating. The collimated light illuminated the grating to obtain the spectral interference signal focused onto a line scan camera through lens L6. The spectra recorded by the spectrometer were mapped to K-space and then processed with a numerical dispersion compensation algorithm. To acquire the spectral interference signal, a line scan camera (L104k-2k, BASLER, Ahrensburg, Germany) was used, with a total of 2048 pixels. The depth-resolved reflectivity profile of the sample was obtained by Fourier transforming the spectral interference signal. The acquired OCT structure images were analyzed  
Figure 1: Schematic of Spectral Domain Optical Coherence Tomography (SLD: superluminescent diode, L1–L6: lenses, M1–M2: mirror, PC: polarization controller). Here, the microscope on the sample arm was used to adjust the seed orientation placed on a Petri dish. The photograph shows a picture of the real system, with the encircled region showing the seed. The bright region on the seed indicates the scan line. A cover glass plate was used to partially compensate for the dispersion introduced by the objective lens in the sample arm. Dispersion was also compensated based on offline correction of the data after collection. to calculate the contrast of the biospeckle. The depth resolution (axial resolution) of the system in free space was calculated as 6 \(\upmu\)m using the following Equation (1), and the lateral resolution was calculated as 22 \(\upmu\)m by Equation (2);  
\[\Delta z=\frac{2 ln{\lambda_{0}}^{2}}{\pi\;n\;\Delta\lambda}, \tag{1}\]  
\[\Delta x=\frac{4\lambda_{0}}{\pi}\;\bigg{[}\frac{f}{d}\bigg{]}, \tag{2}\]  
where \(f\) is the focal length, \(d\) is the beam diameter, and \(n\) is the reflectivity index (\(n=1.4\)). Before the OCT measurement, the seeds were dried with paper towels to avoid moisture on the seeds from affecting the data. To ensure that OCT images of all of the seeds were acquired from the same position, the seeds were needed to be adjusted and fixed in position and orientation before scanning.