72 OBJECT LESSONS IN BOTANY. 
129. With a sharp knife let us make a cross-section (that 
is, a cut square across) of a flower-bud just ready to open ; 
we may thus obrain some such views as are here drawn. 
For example, in Fig. 217, we have the valvate arrangement. 
Here the pieces composing the circle barely touch each other 
by the edges, as in the sepals of Mallows, petals of Lilac, 
valves of a seed-vessel. (See, also, Figs. 218, 219.) 
130. In the Phlox, Flax, Oleander, we find a twisted or 
contorted arrangement of the petals (Fig. 220), where each 
piece overlaps the next, all in one direction. 
131. The bud is said to be imbricated, when some of the 
pieces are wholly outside, covering by the two edges others 
which are wholly inside. But this may take place in various 
ways. See how it is in the petals of the Eglantine, or Apple 
(Fig. 221). Here two petals are outside, two inside, and one 
partly both. In the Tulip, one sepal is outside, one inside, 
and one partly both. And just so with its three petals 
(Fig. 222). 
132. The bud is convolute when each leaf wholly involves 
all that are within it, as do the petals of Magnolia and Wall- 
flower (Fig. 228); and it is vexillary in the Pea tribe, where 
only the outside petal, larger than the rest, infolds them all 
(Fig. 224). 
183. The plicate arrangement is found in monopetalous 
flowers, as in Thornapple, Potato, where the corolla is folded 
in a manner somewhat like a fan. 
129. How do we prepare a bud for examination? What do you under- 
stand by a cross-section? Define the valvate arrangement, with examples. 
130. What estivation do we find in Flax, Phlox, &c.? 
131. What is the imbricated estivation? Describe it in the petals of 
Tulip; Apple; Eglantine. 
132. How are the petals arranged in the bud of Wall-flower? 
133. How in the flower of Thornapple? or Potato? 
