Fig. 4

Early stages of budding in Polyandrocarpa zorritensis. a Schematic summary of vasal budding, depicting the four main steps: swelling, invagination, fusion and double vesicle. b Semi-thin section of a vasal bud at the swelling stage. c Detail of the vascular epidermis on the top side (squared in b). d Detail of the vascular epidermis on the bottom side (squared in b). e Semi-thin section of a vasal bud at the invagination step, showing the invaginating epidermis (black arrows), the movement of the invaginating edges (pink arrows) and the part of the epidermis that goes on to form the floor of the inner vesicle (orange star). f Detail of the bottle-shaped cells at the invaginating hinge points (as squared in e). g Detail of a wedged-shaped cells at the invaginating edge (as squared in e). h Semi-thin section of a vasal bud at the fusion step, showing the inner vesicle floor (orange star), the inner vesicle lumen (green asterisk) and the movement of the fusing borders (pink arrows). i Detailed view of the inner vesicle wall. i’ Close-up of the cilia apex of the inner vesicle cells (as squared in i). j Detail of hemocyte aggregate at the fusion area (as squared in h), showing undifferentiated hemoblasts (green arrows) and granules-containing cells (blue arrows). k Semi-thin section of a vasal bud at the double vesicle stage. l Detailed view of hemocytes located between the inner and the outer vesicle. m Ampullar wall showing absence of cell membrane and cytoplasmic continuity between cells (pink asterisks). n–n’ Contact between an ampullar epidermal cell and a morula cell. Blue arrow shows cytoplasmic continuity (Scale bars. b, e, h, k: 50 µm; c, f, g, m: 10 µm; d, j, l 20 µm; i: 5 µm, i’ 2 µm, n 2 µm, n’ 1 µm) (a ampulla, h hemocytes, iv inner vesicle, l vessel lumen, m mitochondria, n nucleus, ov outer vesicle, t tunic)