20 



MORPHOLOGY 



33. In some Oaks, notably in our Live Oak (Quercus virens), 

 and less so in the Horsechestnut, the two cotyledons coalesce or 

 cohere by their contiguous faces. 

 In some of these cases of hypo- 

 gaeous germination, the short 

 caulicle and plumule are extri- 

 cated from the enclosing coats or 

 husk by the development of short 

 stalks (petioles, 157) to the fleshy 

 cotyledons ; as is seen in Fig. 42, 

 and in most germinating acorns. 

 These petioles are not visible in 

 the seed, but are the first develop- 

 ment in germination. 



34. There are some curious 

 cases in which, while the caulicle 

 remains short and subterranean, 

 the cotyledons are raised out of 

 ground in germination by the 

 formation of far longer stalks 

 (petioles) than those of the 

 Horsechestnut. A singularly dis- 

 guised instance of this kind is seen in Megarrhiza, a genus of 

 Cucurbitaceous plants of California and Oregon, remarkable for 

 their huge root. The large seed has very thick and fleshy 

 cotyledons, and a very short and straight caulicle. In germi- 

 nation, the whole seed is elevated, seemingly in the manner of 

 the bean, upon a stout stem. One waits for a long time expect- 

 ing to see the cotyledons throw off the bursting husk and expand, 

 or else to put forth the plumule from between their bases. But 

 at length the plumule makes its appearance from an unexpected 

 place, coming separately out of the soil. Eemoving this, the 

 state of things represented in Fig. 43 is presented, that of 

 the plumule seemingly originating from the base, instead of the 

 apex, of an elongated caulicle ! But on examination of the cleft 

 from which this proceeds, by making a section of the stem above 

 (showing that it is hollow), and finally by separating the cotyle- 

 dons and gently tearing apart the two short stalks by which they 

 are united to their stem-like support, it is found that the latter may 

 be divided into two (as shown in Fig. 44), even down to the cleft 

 below. This explains the anomaly. The real caulicle has re- 



FIG. 41. Section of a Horsechestnut or Buckeye seed, through the very thick 

 cotyledons and the incurved caulicle. 42. Seed In germination, showing the petioles 

 to the cotyledons, <fcc. 



