418 BOTANY. 



constitute the floral envelopes, or, technically, the perianth. 

 Frequently there is a strong difference between the outer and 

 inner whorls, and in such cases the former is distinguished 

 as the calyx, and the latter as the corolla. 



527. The whorl of stamens (technically the Andrcecium) 

 develops above the upper whorl of the perianth. Each 

 stamen generally consists of a slender, thread-like stalk (fila- 

 ment), bearing upon its upper extremity from one to four 

 pollen-sacs ; this pollen-containing portion, whether one or 

 more celled, is known as the anther. In its development 

 the stamen at first bears a close resemblance to a rudimentary 

 leaf, both in structure and position, and there can be no 

 doubt that it is a phyllome, modified into a pollen-produc- 

 ing organ. Whether the anther is to be regarded as an out- 

 growth of the phyllome, or as its modified upper portion, is 

 doubtful ; analogy would indicate the probability of the 

 former view. There can be bat little doubt that the pollen- 

 sacs are to be considered homologous with the microspo- 

 rangia of the higher Pteridophytes, and the latter are clearly 

 outgrowths (trichomes ?) upon phyllomes. 



528. The pollen- grains are developed here as in Gymno- 

 sperms, from pollen mother-cells ; the latter are differentiated 

 parenchyma cells, lying in or near the axis of the pollen- 

 sacs. Each mother-cell undergoes two divisions (by fission), 

 producing four parts, which become as many pollen-grains. 

 The mature pollen-grain is a single cell, and consists of a 

 mass of protoplasm mixed with oil-drops, starch granules, 

 etc., surrounded by two investing membranes, an outer hard 

 and firm one (the extine), and an inner thin and delicate one 

 (the inline). In the germination of the pollen-grains, they 

 always remain single cells, there being no formation of in- 

 ternal cells (rudimentary prothallium) as in the Gymuo- 

 sperms. The development of the pollen-tube takes place as 

 in Gymnosperms, by a prolongation and growth of the 

 intine, but here the extine is not slipped off in the process, 

 but only pierced in certain thin areas of its surface. Usually 

 but one tube issues from each pollen-grain, but in some 

 cases e.g., (Enothera two or more are sometimes found. 



529. The female reproductive organs (individually the 



